Calling all wiring experts

DPV7070

ForceFed40
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***Warning...longwinded post about electrical follows***

Ok gents, I'm a pretty patient, smart (maybe, although I do fly a pretty complex machine), and meticulous person, but I'm starting to get stumped on this one...primarily because of the "PO wiring mod." My truck is 6/72 with a 1970 350 conversion....So here's the back story:

I decided I wanted to replace all my rear brake lights (so they would match), back up light, and markers with new OEM units. Easy day right? Ok, so I remove the old ones, scuff up all the grounds so they're nice and clean, then replace them. I check the operation of each thing as I'm replacing and they're all working. So far I had replaced both tail lights, the back up light, and the rear side marker lights. Everything worked as advertised. Well I start looking at the rear loom and the PO had hacked in a trailer harness (which didn't work). So I rewired the rear loom per Coolerman's "cleaned up" diagram (thanks dude!). Pretty simple. Got her buttoned up, yep...everything still works. Feeling pretty good so I go grab the wifey so she can admire my handywork. She comes out. Everything works. Wife clearly in awestruck state...

Fast forward 30 mins ;). I come back and just for grins I want to see it work. Everything on the rear works, but now the headlights wont work. Hmm. I check a few things including the headlight switch (cleaned and reassembled) and now I have no brake lights, but I have headlights. I try the hazards. I have hazards, but after turning them off I have no turn signals and no brake lights. It progressively got worse until the only thing that would work consistently was the headlights and occasionally the turn signals. I never could find a pattern of turning things on and off that resulted in them working consistenly. Using a test circuit I energized the tail loom and it all works correctly (I knew this already since I had seen it with my own two eyeballs). I check the grounds and they were good. Reground the battery, etc.

Bottom line I'm not getting power to the rear brake lights via the solid green wire. So I check the brake switch...aha!

2dim7q1.jpg


One of the connectors is broken off. Ok, so that's got to be the problem right? Well, I hold the broken connector back on, depress the brakes, and still nothing (though now that I think about it seeing the picture that corrosion is pretty bad, probably should scuff it up). I've got a new stop light switch on order. Continuing my troubleshooting I pop the instrument panel and notice there's some serious chaffing on the main loom. I peel it back and this is what I found:

2iwaj5g.jpg


So, a really chaffed Black/White (starter circuit), and 3 parted wires: black, black yellow (oil pressure sender???), blue yellow (????).

And finally it looks like someone hacked in a cluster bulb (this doesn't look like a factory splice):

15mnx3s.jpg


This dang bulb lights up anytime the key is in the acc or ign position (it's always on while driving...hence, someone put black electrical tape over it). Its wire runs out the firewall next to the clutch master cylinder and is grounded somewhere in the engine bay.

One other thing to note is there was a single pole, double throw switch (on/off) that was wired in coming from the turn signal, through the switch, then back into the turn signal loom (above the switch there's a sticker that's been painted over that says <Tow----Drive>. I eliminated this switch (since I got rid of the trailer harness). I don't think this has anything to do with anything since everything worked after removing the switch.

So here's my questions:

1) Am I barking up the right tree as far as troubleshooting. Is the stop light switch the key?
2) Obviously I need to fix the chaffed wires, but what do they go to exactly (I took a WAG at it).
3) Any ideas as to what that light is? (I thought it was the hi/lo for the headlights, but that doesn't seem to be it).

I'm open for comments, criticism, whatever as I'm completely stumped right now. I've troubleshot everything I can think. Stared at wiring diagrams forever, and just wanted to see if anyone has had a similar experience. I'm located in San Diego if anyone can offer some help.
 
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So here's my questions:

1) Am I barking up the right tree as far as troubleshooting. Is the stop light switch the key?
2) Obviously I need to fix the chaffed wires, but what do they go to exactly (I took a WAG at it).
3) Any ideas as to what that light is? (I thought it was the hi/lo for the headlights, but that doesn't seem to be it).

.

1. Probably not. It should only have two wires: Red/white = power in from fuse. Green/white power out to turn signal switch. The turn signals should work any way even if the switch is bad.

2. You figure it out from the color code and location. Ideally, you would find the other end of the wire. The schematic diagram shows where all the different color wires start and end. Black/yellow is a key on engine power wire, like used for the ignition coil and the voltage regulator. Green/yellow is a right turn signal, either front or rear. Black, I forget, but you can find it on the schematic.


3. It looks like a dash panel light.

A short list of what works and what doesn't would be helpful.

It sounds like you still have intermittent problems, right?
 
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could the light be your brake light? if the handbrake is on with the ignition on or if there is a fault in the brakes then the light would be on.

My 1978 Black Yellow is the oil pressure sender and the blue yellow is from the wiper switch to wiper motor.
the only black wire I have is the ignition coil which would obviously not be where you found yours. Maybe this was a patch wire! your extra bulb has black wires maybe that was all the DPO had to use!

it looks from your photo the light is spliced into a predominantly yellow wire and the only ones n my loom like that are signal wires to the Oil or temp or fuel!
 

DPV7070

ForceFed40
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1. Probably not. It should only have two wires: Red/white = power in from fuse. Green/white power out to turn signal switch. The turn signals should work any way even if the switch is bad.

2. You figure it out from the color code and location. Ideally, you would find the other end of the wire. The schematic diagram shows where all the different color wires start and end. Black/yellow is a key on engine power wire, like used for the ignition coil and the voltage regulator. Green/yellow is a right turn signal, either front or rear. Black, I forget, but you can find it on the schematic.


3. It looks like a dash panel light.

A short list of what works and what doesn't would be helpful.

It sounds like you still have intermittent problems, right?

Pinhead, thanks for the help...

1) Yep, you're right on. The turn signals still worked. I think my main priority is to find where the power in the green wire is terminating since it's obviously not going back to the tail lights.

2) One of the parted wires is Blue/Yellow, not GY...this is the one I can't find on the wiring diagram. In later diagrams it's in the window washer/wiper circuit.

3) Now that I think about it, that light may be for the "Brakes" light. My e-brake currrently has no guts, so the switch maybe doing something funky. I'm rebuilding the e-brake this weekend so I'll check it out.

Thanks again everyone.
 
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Blue/White

I think that blue/white wire might be for emissions. If it drops out by the voltage regulator that's what it is.

The Black/Yellow should be 12v switched to the fuse box.

The parking break switch should have two green/yellow leads. It does not affect the operation of the tail lights.
 
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If you have a one wire alternator, the light may be to keep current from backfeeding through the system after the key is turned off preventing the rig from turning off.
 
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AFAIK, there is no blue/yellow wire. The only blue used is light blue. Wire colors change with time and exposure to the environment, so chances are it is an original green/yellow wire (as it looks to me). Besides the turn signals, there are also front drive indicator light and horn relay wires that are green/yellow according to the '72 schematic.
 

DPV7070

ForceFed40
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If you have a one wire alternator, the light may be to keep current from backfeeding through the system after the key is turned off preventing the rig from turning off.

I think you may be on to something here, I definitely have a 1 wire alternator.
 
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Not sure why they would cover the bulb though. My dad's 40 has the same set up. If the light comes on while it is running it means the alt is not charging.
 
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It's not a charge indicator light. It appears it's used as a resistor for the 1-wire alt as bsilva132 stated above. I have a 1-wire as well but I'm using an EZ harness so it's not needed. You could replace it with a true resistor (not sure what value you'd need off hand) or keep it like it is.
 
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It looks like a generic gauge or cluster lamp. It may be a charge indicator lamp for a GM alternator, but this is not a 1 wire alternator. It is just an internally regulated alternator and the excitor wire runs through a charge indicator lamp, but the lamp can be replaced with a resistor that has the same resistance as the lamp. A 1 wire alternator only has the one large wire that goes to the battery.
 
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is there a light bulb with wires going to it in you're parking brake indicator light? I know that mine was wired funny when I got the truck and if they assembly was taken apart by someone maybe the light was always on?

When I first got my truck the parking brake indicator light came on every time I stepped on the brakes with the running lights on... it was very annoying when driving at night. Perhaps PO had a similar problem and decided this was the best fix?
 

DPV7070

ForceFed40
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Well, I've got an update. I removed the hazard switch last night and cleaned all the contacts, etc and reinstalled it. Once I did that I had hazards, brake lights, headlights, and no turn signals...What the heck? Pushed hazard switch in to turn off, then back on and I'm back to only having headlights. Dang! I also noticed that after having my key in the IGN position, not start, that my coil was freaking overheating. It's probably wired incorrectly as well, so now I'm trying to figure out what the PO (should be called POS) did. I think I need to walk away from the wiring for a little bit and button up the parking brake rebuild I've got going on.

In other news I scored an all original (looks to have been a spare) OEM steelie with a practically unused Dunlop SnowCruiser 78. So, now I have 5 steelies that I'm going to blast and powdercoat. Additionally the tire shop on base was having a huge sale so I went ahead and pulled the trigger on 5 33x10.50 BFG AT's (road hazard, lifetime rotation, balance, etc) out the door for $850. So, happy I saved a little on that. Anyways, I appreciate all you guy's help. Keep it coming...
 
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DPV7070

ForceFed40
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Well I replaced the brake switch and everything seems to be working fine now. However, I think I may still have a loose wire near the fuse block because after I saw everything working I bolted it back in and went back to headlights only. I ran my finger down all the fuses to make sure they were seated and tried it again. Everything worked! Now on to sorting out the coil and ignition which I think was improperly installed due to the coil getting hot as hades.

Still haven't figured out what the blue/yellow wire is. It's definitely blue/yellow, there's a blue/white in the same loom and there is a distinct difference. The aftermarket light is for sure an idiot light (maybe reverse flow inhibitor) for when the alternator is not charging (the wire runs directly to stud on the back of the alternator).
 
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Coil heating up with the key left on is normal.
You are still having intermittent power feed problems, so it is time to clean and check all the connections at the fuse block and back to the battery. The fuse block is a frequent source of problems.
 

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