Universal wiring harnesses?

SonOfTheGrim wrote:You know what they say: Universal fit means universally doesn't fit anything, right?

Absolutely right. My other concerns would be that for that price they don't supply enough wire length, and/or worse, the wire gauges are too small for heavy-draw circuits like power windows. Any way you slice it, you will be doing extra fabricating like lengthening wires and finding a new way to mount the fuse box, which will not mount the same way your old one does, even with a Painless harness. So in turn you will also have to come up with a new way to secure the firewall bulkhead connector, which is held in place by the stock fuse box. The point is, you can make anything work, but it will be a bigger job than anyone tells you, even the Painless people, because there will be mods you'll need to make for your particular car, especially if you go off script and add a bunch of extra features your car didn't come with.

My other suggestions would be:

1) Get as many circuits as possible to start -- easier to not use them now and have them available for later than to try to add them in afterward.

2) Use self-resetting breakers (not fuses) for high-draw things like power windows, seats, locks, etc.

3) Make sure you have some other automotive electrical experience. This is a big job, and it will be a lot easier if you've already got some other electrical projects under your belt.

FWIW, another route is to use an existing harness from another car. I used the harness from a 93 Caprice wagon and it worked out great, but I had a lot of extra work to do to relocate the fuse panel, track down appropriate connectors & terminals, etc. However, it gave me the ability to add things like ABS, daytime running lights, power mirrors, etc. I could even add in airbags later if I feel the need for a challenge.

I should probably add more circuits but I don't want to rewire the whole car.

How would you add more circuits to the stock setup? Do you add an additional board and run a wire from the alternator/battery? Or would you piggy back off of the stock board some how to make sure it only runs when the car is on?

The first thing to consider when adding something electrical is the expected current draw of the thing you're trying to add.  Your primary options would be:

1. Tap into an existing circuit.  You could get away with this if you are adding something with a very small current draw.  For example, you could simply splice an LED into the instrument panel lamp circuit, especially if you've lowered the normal current drain by switching all the other lamps on the circuit to LEDs.  In this case, you've drastically lowered the possible maximum amount of juice, so there's capacity to spare.

2. Add a new circuit. This will involve exactly what you describe above -- a new feed from the batt/alternator (or ignition switch or existing fuse block) running to an inline fuse or a mini-fuse block.

The next thing to consider is when the thing needs to have power.  If the answer is 'always' (i.e. even with the ignition off), you can run straight from the batt/alternator to the fuse, and then to the device.  If the answer is 'only in run' or 'only in accessory', then you are looking at splicing directly from the appropriate feeds from the ignition switch, then to the fuse, then to the device.

Last thing then is wire gauge.  This will be determined by the total amount of current the circuit is expected to carry for any length of time.  Too small a wire gauge, and the wires will run too hot and introduce too much resistance, which will play hell with electronic devices and sensors.  I tend to go more conservative than the factory, so I use roughly this scale:

1A or less = 20ga
1A to 5A = 18ga
5A to 10A = 16ga
10A to 15A = 14ga
15A to 20A = 12ga
20A to 30A = 10ga

Also be aware that the ground wire will need to be the same gauge as the feed.

And a word of caution: Under no circumstances should anyone just add stuff to an existing factory circuit and put in a larger fuse.  While the fuse will allow the larger amount of current through, the wires were sized according to the original expected load.  Pulling more juice through a wire that's too small will create heat.  LOTS of heat.  Possibly even enough to melt the insulation or wiring, or even start a fire depending on how much current you're trying to stuff through them.

I am very interested in this idea; using a newer harness from a different car. I would love to know more about how you did it.
I got under the dash today to figure out why my freshly installed motor won't crank and found that my harness is completely screwed. It is so cut up and sliced I don't think it's even safe to use.

Do you have any pictures or a thread about using the caprice harness?

Looking around on eBay I found this.

Does that look like an EZ harness to anyone else?

SonOfTheGrim wrote:I am very interested in this idea; using a newer harness from a different car. I would love to know more about how you did it.
I got under the dash today to figure out why my freshly installed motor won't crank and found that my harness is completely screwed. It is so cut up and sliced I don't think it's even safe to use.

Do you have any pictures or a thread about using the caprice harness?  

Other than that shot of the fuse panel, I didn't really take any photos.  The fuse panel was the most interesting thing visually -- I figured, who wants to look at pictures of wires?

In addition to the 93 Caprice harness, there's also a fair portion of 86 Camaro for the TPI grafted in, as well as a LOT of custom stuff (Vintage Air, overhead console, keyless entry, power windows/locks, lighting subpanel, etc).  Basically I went so far off script that I didn't think a thread would be as helpful as just assisting where possible on people's individual issues/projects/ideas.

So if you want pictures/diagrams of something specific I did (or you want to do), I am happy to provide on an as-needed basis.

SonOfTheGrim wrote:Looking around on eBay I found this.

Does that look like an EZ harness to anyone else?

I wouldn't start with that one.

What are your goals?  Are you looking to just replace your worn harness with something more reliable, or are you looking to do a lot of custom mods down the road?  If the latter, what kind of features were you looking to add in?

If all you want to do is make the car work again, I'd probably go with a prebuilt harness like Painless or equivalent.  It will still require a fair amount of work, but not as much as grafting in the harness from another car.  It's designed to handle the usual stuff your car might need.

On the other hand, if you're planning to go hog wild with mods like I did, then it makes more sense to start with a 91-96 Caprice/Roadmaster (or other GM full size vehicle from about that period) harness -- these are very similar to our cars, have a lot of interesting factory features, and -- most importantly -- are much easier to modify than a prebuilt harness.  But make no mistake, they're more work, and you will need the factory service manual for the donor vehicle in order to understand what goes where.  However, you will gain huge insight into how things work, and therefore be able to do things no prebuilt harness will handle.

So the question is -- what's the plan?

My goal for the wiring is to update it to modern fuses and get away from those glass ones (of which I broke 2 last night because the ends were rusty and stuck), and to get rid of every single cut and splice and hack done by previous owners. I'm not going for stock but simple and reliable. I want good clean wire, good clean connectors, and good clean routing. As far as future projects and additions, I want to eventually do power windows and locks and I have a (driver) electric seat I will be installing. I really don't want anything crazy. Maybe a good stereo, but not like subwoofers and amps. Just a good set of 4 speakers and head unit.
The thing that draws me to the unliversal harnesses is the modern fuses and new box clearly labeled as well as the actual wires being labeled every few feet. Why doesn't every car manufacturer do this?

I know that harness from the truck wasn't a good starting place, I just thought it was funny. But considering using a harness out of a different car has got me curious. What were your criteria for looking for a harness? What things did you look for in the car you were taking from?
I think my biggest thing to consider is the fact that both of my cars have HEI electronic ignition from the factory. This has been the biggest challenge when looking for wiring diagrams and such because the diagrams all have the old coil style, even for a 76 or 77.

So if I were to look for a harness from, say, a 78+ chevy truck how far off would it be layout and color wise? I think anything after about 1976 would have HEI and be less of a modification.

Here is what I am dealing with under my dash. Someone invested in a spool of yellow wire which they used for EVERYTHING, there are random bad splices to and from everything, things taped up and hanging down. You name it, its under there.


I also think my ignition switch might be bad because I get power to the switch but not to the starter soleniod. That was my dad's diagnosis tho. He's the electrician.

SonOfTheGrim wrote:My goal for the wiring is to update it to modern fuses and get away from those glass ones (of which I broke 2 last night because the ends were rusty and stuck), and to get rid of every single cut and splice and hack done by previous owners. I'm not going for stock but simple and reliable. I want good clean wire, good clean connectors, and good clean routing. As far as future projects and additions, I want to eventually do power windows and locks and I have a (driver) electric seat I will be installing. I really don't want anything crazy. Maybe a good stereo, but not like subwoofers and amps. Just a good set of 4 speakers and head unit.
The thing that draws me to the unliversal harnesses is the modern fuses and new box clearly labeled as well as the actual wires being labeled every few feet. Why doesn't every car manufacturer do this?

I hated my barrel fuses too for the same reasons, which was also a motivator for me (along with other things, more on that below).  It sounds to me like a prebuilt harness will suit you pretty well then.  Get one with 20 or more circuits, and it should include things like breakers for power seats, windows, etc -- like I mentioned earlier, it's better to get those additional circuits now than to to try to add them in later.  There will still be some work involved, but the fuse panel end will already be done.  Your concerns will be where/how to mount it, how much of the old harness to keep and where to splice, and tracking down vehicle-specific connectors and such that the universal harness won't come with.  

SonOfTheGrim wrote:I know that harness from the truck wasn't a good starting place, I just thought it was funny. But considering using a harness out of a different car has got me curious. What were your criteria for looking for a harness? What things did you look for in the car you were taking from?

I came at it from a different direction, really.  I didn't go looking to replace the entire harness from the outset.  I actually started with the TPI, which needed its harness almost completely rebuilt, and it taught me a LOT.  Then I was determined to retrofit ABS after I learned how similar the 91-96 Caprice cars were to ours, and that the ABS system was standalone.  From there, then, it was a short leap to grafting in the rest of the harness from the Caprice, since there were a lot more things I wanted to add, and the stock harness would simply never support it, even if it had been in good shape.

SonOfTheGrim wrote:I think my biggest thing to consider is the fact that both of my cars have HEI electronic ignition from the factory. This has been the biggest challenge when looking for wiring diagrams and such because the diagrams all have the old coil style, even for a 76 or 77.

Actually, HEI is the least of your worries.  It's incredibly simple -- one 16ga feed wire that's hot in Start and Run.  That's it.  Just one of the many reasons people upgrade to HEI if they don't already have it.  The universal harness is even likely to have a circuit for that already (if it contains an engine harness).  Though it does surprise me that you're seeing post-74 wiring diagrams with points/coil -- my understanding is that all GM vehicles from 75 and up had HEI, so you'd think they would have updated the diagrams.

SonOfTheGrim wrote:So if I were to look for a harness from, say, a 78+ chevy truck how far off would it be layout and color wise? I think anything after about 1976 would have HEI and be less of a modification.

GM has been very consistent with their wiring for decades across all their models -- same colors, gauges, and circuit numbers.  Even the striping.  They simply added more as they needed them.  For example, many of the circuits in the stock G3 harness are the exact same color, number, and gauge as in the 86 Camaro and 93 Caprice I used, and also an early aught-something Grand Am harness I bought just to have extra lengths of wire.  So in theory, any GM vehicle could provide a donor harness.  I'd look for condition, wire length (a Chevette harness would likely be too small), design of the fuse panel, number of factory features, and availability of the factory service manual (which will be critical).

SonOfTheGrim wrote:Here is what I am dealing with under my dash. Someone invested in a spool of yellow wire which they used for EVERYTHING, there are random bad splices to and from everything, things taped up and hanging down. You name it, its under there.

Yeah, all the same color is the first thing you DON'T do.  You could repair it by tracing each of the 'fixes' and replacing it with the proper color and gauge of wire, but you're right -- this is an optimal time to upgrade the whole thing.

SonOfTheGrim wrote:I also think my ignition switch might be bad because I get power to the switch but not to the starter soleniod. That was my dad's diagnosis tho. He's the electrician.

That's possible, but there could be other causes, too.  I'll go back and look at the diagrams we have posted in the sticky for the electrical section and see where else you might look.

Well I haven't found a harness yet or decided to buy a new one. But in the meantime I am working through the mystery of my harness and trying to figure out what the PO was thinking and what some of the additions and subtractions are. I have some pictures if anyone can shed some light for me.

First here is my engine harness from the junction block at the firewall. As I understand it the 73-75 models use a pink wire going to the coil and a purple wire going to the starter solenoid. Well my 77 has a tan wire going to the HEI and a pink wire going to the starter sol (this is how the harness was set up but I wonder if the PO wired these backwards).
I am also confused about the fusible link coming from the hot wire terminal because why do you need a fusible link if you have a fuse in the fuse box???


Next is back to under the dash. This silver cylinder next to my fuse panel, it just has the blue connector plugged into BAT and the blue connector at the bottom of the screen has a yellow wire plugged into it but it is cut about a foot down and goes nowhere.


My neutral safety switch on the column has the green and pink connector plugged in but I can see another place for a double connector but nothing that looks like it plugs into it. I *think* it is supposed to have purple wires plugged into it?


This. What the hell is this?


This is the last question for now. I am sure everyone is getting tired of my goings on. I can't seem to find anything on any wiring diagram with a gray, black, and yellow connector.



Again I thank everyone for the information. You people are incredible. By the time I get through this puzzle of a car I'll probably be an expert at wiring and a whole lot more.
Hopefully these questions will keep me busy for a while. I am at this point just trying to get the damn thing to crank.

I have also concluded that my entire dash is going to come out and be repaired/strengthened as it is loose and wobbly and not properly fastened at all.
Another endeavor, maybe for when I get my new harness.

SonOfTheGrim wrote:
First here is my engine harness from the junction block at the firewall. As I understand it the 73-75 models use a pink wire going to the coil and a purple wire going to the starter solenoid. Well my 77 has a tan wire going to the HEI and a pink wire going to the starter sol (this is how the harness was set up but I wonder if the PO wired these backwards).
I am also confused about the fusible link coming from the hot wire terminal because why do you need a fusible link if you have a fuse in the fuse box???

SonOfTheGrim wrote:My neutral safety switch on the column has the green and pink connector plugged in but I can see another place for a double connector but nothing that looks like it plugs into it. I *think* it is supposed to have purple wires plugged into it?

I'm at work with a full plate today, so I'll tackle these one at a time as time permits.

Once the battery connects to the starter, we get to the feeds that go to the rest of the car's electrical system.  The primary is the fat red wire (10ga), which is protected by the tan fusible link from the starter's 'B' terminal.  Since we are not at the fuse box yet, we have no protection for this wire against a short.  That's what the fusible link is for -- it's basically a wire 4 sizes smaller than the wire it protects, and its sole job is to burn up first before the entire red wire does (and anything else on that circuit before the fuse box, such as the ignition switch) in the event of a short between here and the fuse box.  The fuses in the fuse box only protect circuits AFTER the fuse box.

The red wire goes from the starter to the horn relay post to the right of your brake booster.  This is the major distribution center for power to other circuits.  Since we still haven't reached the fuse box, there are more fusible links here, and one should be a black 16ga lead that runs to the bulkhead connector on the firewall -- on the inside of the cabin it becomes a red 10/12ga feed to the ignition switch.  (It also splices off to other places, but we only care about ignition for now.)  Assuming these are intact, you should have power to the ignition switch.

Here's your starting problem.  From the ignition switch we should have a purple 12ga wire with a double white stripe that runs to the backup/neutral switch just like you suspect.  The other side then is a plain 12ga purple wire that runs back to the bulkhead connector and then to the starter 'S' terminal.  Since the purple wires are not connected to the B/N switch, no juice ever makes it to the starter.  The pink and lt green wires are for your backup lamps.  Do you have the purple/purple wires with a connector hanging loose somewhere?  Or are they gone?

The HEI is typically fed via the ignition switch so that it's only hot in Start and Run modes.  If it's connected directly to the starter, it's hot all the time, even when the car is off.  Shouldn't be a huge deal, but you may experience run-on even after you shut the car off, since it still has juice even when you turn the key off.  Also, the wire should be minimum 16ga.  Anything smaller and the HEI does not get enough current to perform at its best.

More soon...

SonOfTheGrim wrote:This is the last question for now. I am sure everyone is getting tired of my goings on. I can't seem to find anything on any wiring diagram with a gray, black, and yellow connector.

This for the stock radio. Yellow is primary radio power from the fuse box (hot in Run and Accessory). Grey is power from the instrument panel circuit so it lights up when you turn on the headlight switch, and black is ground.

SonOfTheGrim wrote:Next is back to under the dash. This silver cylinder next to my fuse panel, it just has the blue connector plugged into BAT and the blue connector at the bottom of the screen has a yellow wire plugged into it but it is cut about a foot down and goes nowhere.

Don't know specifically what it was for, but sometimes the factory would plug in optional accessories into the spare taps on the fuse panel rather than have them built into the harness itself. For example, my rear defogger had a similar connector that simply plugs into the IGN port below the BATT one. Since that one's plugged into the BATT terminal, whatever it was had constant power even with the ignition off. The silver canister would likely be a ballast resistor/condenser type thing, which would indicate to me that it probably had something to do with the radio to filter out interference. In any event, if it ain't hooked to anything else, pull it out.

SonOfTheGrim wrote:This. What the hell is this?

Okay, that's a head-scratcher for me. The thing on your fingers looks like a transformer, but for the rest of it I got nothin'. Maybe someone else here has seen one.

Where do the wires go? Maybe we can figure it out that way...

Don't get in a hurry for me. After all this is just a project. Like I said, it's a puzzle to unravel, but that's part of the fun right?

I won't be back home today to look at anything but I'll get back to you tomorrow.

I used the Painless 69-74 GM Muscle car 18 circuit harness in my 73 Monte.  

I found it on ebay for $350 from a seller whose project never happened.

Well worth the money imo.

You got any pictures or advisory tidbits for someone like me? I still can't see paying that much for my budget build but surely it can't be a far cry from the universal harnesses I am looking at, aside from the preinstalled connectors and lengths of wire.

I am hoping I can reuse my stock connectors because I found these GM 56 Series Terminal Ends. I am also figuring out how to use the engine bay junction box without using my stock fuse block so I can keep the plug n' play setup.

SonOfTheGrim wrote:I am hoping I can reuse my stock connectors because I found these GM 56 Series Terminal Ends. I am also figuring out how to use the engine bay junction box without using my stock fuse block so I can keep the plug n' play setup.

The type 56 connectors are used in a few places, most notably the bulkhead connector on the firewall that you're referring to.  You will also want to get a supply of the 18-20ga and the 10-12ga ones.  To do an electrical system, you're going to need a fair amount of spare parts.  Your shopping list should look something like this:

• Type 56 terminals
• Type 58 terminals (typically used for relays)
• Type 59 terminals (like 56, only larger for higher current)
• Weatherpack connectors, terminals & seals (completely sealed against moisture)
• Metripack connectors, terminals & seals (similar to Weather pack, but come in assorted sizes depending on wire gauge)
• Molex connectors & terminals (generic DIY connector for in-cabin work, can be used underhood with optional water seal)
• butt splices (preferably bare, but you can also strip off the shielding yourself)

You will need all connectors/terminals/splices in multiple sizes from 10ga to 20ga.  

You will also need wire, in just about every color and gauge from 10-20.  You can buy lengths from suppliers, but an easier route is to pick up an actual GM harness out of a car off ebay (the longer the better), then cut it up as needed.  Since GM was consistent with their harnesses, this should give you most of the colors/striping in the sizes you will need.  If you just buy lengths of wire, also get colored Sharpies and paint markers to duplicate the striping.

Spend a few bucks for a good soldering iron -- the cheapos won't be able to heat more than two or three 16ga wires.  Also, get the thinnest rosin-core solder you can find.  Avoid plumbing solder (acid-core).  Use butt splices to join wires, crimp them and then give each side a dab of solder (crimping alone will not hold).  Same with connectors -- crimp and solder (just a dab to hold it secure).

Ditto on electrical tape -- get the good stuff, as the cheap crap will unwind over time.  Tape every unshielded splice after crimping/soldering.

Get a set of picks if you don't already have them -- this will allow you to depress the tang on the terminals to pull them out of the housings so you can reuse the housings.  They will also come in handy for digging the weatherproofing grease out of the bulkhead connector, of which there will be a lot, and it will have hardened.

Here are some sites you can go to for supplies, in no particular order:
mouser.com
waytekwire.com
repairconnector.com
texasindustrialelectric.com
digikey.com

and, of course, ebay.

Lastly, get this.  It will save your sanity.

Good advise from thatfnthing!

The Painless harness did not have the end connectors attached, you have to trim the harness to the length you need and crimp on correct terminals/reuse some of the plastic outer plugs.  

The Painless harness for 69-74 GM mounts just like the stock fusebox with the correct underhood harness and bulkhead connector going through the firewall.  

I would try to find a secondhand new Painless harness. I looked for a few months and a few listed on ebay $100+ below retail/summit price.

Waytek was also a huge help with my project.

Ok I'll keep a lookout for one. EBay is my playground so if there is one I'll find it.

Well I found the plug with purple wires tucked up over the steering column. I pulled it out and the end was taped up and under all the tape was a jumper to have it bypass the neutral switch. So I am thinking that this car has had a previous problem with cranking.
I plugged it back into the neutral switch and still nothing.
Something else I remembered and found from before I put the engine into the car: a thick, green wire that was running through the firewall that both my dad and myself scratched our heads at and then cut it without another thought.
Well that wire was under the dash and spliced into the purple and white wire coming from the ignition switch. I am thinking that this wire was previously ran to the starter solenoid, maybe because the neutral safety switch is bad?
 I am wondering (just to experiment) if I were to reconnect that wire to the starter sol if I could crank the car.

And that jumble of stuff that even had you, fnthing, wondering? It was hanging by one red wire that I traced to the back of the radio (factory original if you believe it) and I believe it was something to do with an old CB radio or something. There was the remains of some kind of broken plastic frame screwed to the bottom of the dash so something used to be there. That mess is gone now.

73CopperMonte wrote:The Painless harness for 69-74 GM mounts just like the stock fusebox with the correct underhood harness and bulkhead connector going through the firewall.

Interesting. I had never seen one live, and the photos they show are always of some generic unit, so I *assumed* it didn't mount in the old location. I know I have seen others that do not. Maybe that's the justification for the higher price.

SonOfTheGrim wrote:Well I found the plug with purple wires tucked up over the steering column. I pulled it out and the end was taped up and under all the tape was a jumper to have it bypass the neutral switch. So I am thinking that this car has had a previous problem with cranking.
 I plugged it back into the neutral switch and still nothing.
Something else I remembered and found from before I put the engine into the car: a thick, green wire that was running through the firewall that both my dad and myself scratched our heads at and then cut it without another thought.
Well that wire was under the dash and spliced into the purple and white wire coming from the ignition switch. I am thinking that this wire was previously ran to the starter solenoid, maybe because the neutral safety switch is bad?
 I am wondering (just to experiment) if I were to reconnect that wire to the starter sol if I could crank the car.

The PPL/WHT wire is the 12v supply for the starter when you turn the key.  Technically that "jumper" should have allowed juice to flow from the ignition switch down the PPL/WHT wire directly to the PPL wire, and then to the starter 'S' terminal.  I'm guessing they botched that up somehow and spliced in the green wire you found.  Would have been simpler to just replace the B/N switch (or just adjust it, sometimes they get out of whack).  So if you reconnect the green wire, does it crank?

If it were me, I'd put it back to the way it was intended to work, and then do the following tests with a multimeter:

1. Test the PPL/WHT wire terminal from the plug to ground. When you turn the key to Start, does it read 12V?  If not, problem is at the ignition switch (assuming they didn't mess up that wire again somewhere else).

2. If #1 worked, connect a jumper wire from the PPL/WHT plug terminal to one of the terminals on the B/N switch.  Make sure the car is in Park, test the other switch terminal to ground while turning the key.  It should show 12V.  If not, the B/N switch is bad or out of adjustment.

3. If #2 worked, the last leg is PPL to the starter.  Test the PPL wire at the starter end to ground while having someone turn the key.  As before, you should get 12V.  If not, that wire is damaged or severed somewhere, possibly broken where it passes through the bulkhead connector.

Or you could just put the green wire back.

SonOfTheGrim wrote:
And that jumble of stuff that even had you, fnthing, wondering? It was hanging by one red wire that I traced to the back of the radio (factory original if you believe it) and I believe it was something to do with an old CB radio or something. There was the remains of some kind of broken plastic frame screwed to the bottom of the dash so something used to be there. That mess is gone now.

Yep, that's what I would have done.

Now that I'm thinking about it, I want to say the PPL wire from the B/N switch to the starter is broken somewhere.  Their 'fix' makes sense if:

• The car doesn't crank, so they suspect the B/N switch and jumper it to bypass.

• The car still doesn't crank, so they splice the GRN wire into the PPL/WHT wire and run straight to the starter.

Still not the right way to fix it, but it explains their kludge.  Expect a problem with the PPL wire.

We used to tap into that purple wire for a kill switch, years ago.