Universal wiring harnesses?

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Re: Universal wiring harnesses?

Post by thatfnthing on Tue Oct 20, 2015 1:15 pm

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...


Last edited by thatfnthing on Tue Oct 20, 2015 1:53 pm; edited 1 time in total
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Re: Universal wiring harnesses?

Post by thatfnthing on Tue Oct 20, 2015 1:31 pm

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.
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Re: Universal wiring harnesses?

Post by thatfnthing on Tue Oct 20, 2015 1:40 pm

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.
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Re: Universal wiring harnesses?

Post by thatfnthing on Tue Oct 20, 2015 1:45 pm

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...
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Re: Universal wiring harnesses?

Post by SonOfTheGrim on Tue Oct 20, 2015 4:58 pm

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.
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Re: Universal wiring harnesses?

Post by 73CopperMonte on Tue Oct 20, 2015 10:05 pm

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.

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Re: Universal wiring harnesses?

Post by SonOfTheGrim on Wed Oct 21, 2015 3:13 am

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.
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Re: Universal wiring harnesses?

Post by thatfnthing on Wed Oct 21, 2015 9:37 am

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. Smile
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Re: Universal wiring harnesses?

Post by 73CopperMonte on Wed Oct 21, 2015 9:09 pm

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.

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Re: Universal wiring harnesses?

Post by 73CopperMonte on Wed Oct 21, 2015 9:11 pm

Waytek was also a huge help with my project.

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Re: Universal wiring harnesses?

Post by SonOfTheGrim on Wed Oct 21, 2015 11:15 pm

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.
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Re: Universal wiring harnesses?

Post by thatfnthing on Thu Oct 22, 2015 8:51 am

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.
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Re: Universal wiring harnesses?

Post by thatfnthing on Thu Oct 22, 2015 9:04 am

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. Smile


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.
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Re: Universal wiring harnesses?

Post by thatfnthing on Thu Oct 22, 2015 10:54 am

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.
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Re: Universal wiring harnesses?

Post by 73CopperMonte on Thu Oct 22, 2015 7:59 pm

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


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Re: Universal wiring harnesses?

Post by 73CopperMonte on Thu Oct 22, 2015 8:02 pm

thatfnthing wrote:
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.

Yes, fusebox and bulkhead through firewall bolt into stock location. Its a nice harness and worth the money imo.

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Re: Universal wiring harnesses?

Post by SonOfTheGrim on Sun Oct 25, 2015 10:12 pm

SHE LIVES!

She finally took her first breath! I got it to turn over.
I decided that I'd fix the cut wires and gnarled splices to trace back the actual problems that made the PO start cutting the harness up. After butt splicing and spade connecting some of the obvious stuff and fixing the purple and white wire I made a good clean jumper with spades and bypassed the neutral safety switch, reached up and turned the key and... the motor turned over! Wiggled everything around and tried a couple more times to make sure there wasn't a cut wire somewhere else. So that's a huge step.
Now I just have to get everything done in the engine bay and maybe I can take it for a ride down the road.

It seems like most of these electrical problems are because of halfassed fixes the first time around. Maybe if I keep tracing I'll find the initial problem.
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Re: Universal wiring harnesses?

Post by SonOfTheGrim on Sun Oct 25, 2015 10:20 pm

And again I want to thank everyone for all the amazing help. You guys know your stuff and Thatfnthing, you particularly are just awesome at this stuff. I am smarter for conversing with you. Thank you.

I am going to keep adding to this thread as I unravel more and get farther.
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Re: Universal wiring harnesses?

Post by thatfnthing on Mon Oct 26, 2015 9:05 am

Always happy to help. Glad you're making progress.

However, when possible I'd replace or adjust that neutral safety switch so it works like it should. Just my $0.02.
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