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Old 04/29/2017, 07:36 AM   #1
TexAg
 
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Headlight wiring harness

Advise wanted -

I'm having some charging issues, that as best I can tell can be traced back to a
resistance or breaks in the charging circuit. Specifically the wires that are part of the voltage regulator plug are frayed and corroded. (Alternator and VR all test good, but the juice doesn't get to the battery. I get 13.4v +/- at the A terminal of the VR, but it only shows 12.5 at battery.)

It appears that these are all part of the headlight wiring harness, so here are my options.

1) Leave it as is and install a 1-wire alternator with internal regulator. I figure that I can leave all of the factory wiring in place, and reverse this modification in the future if needed.

2) Replace the headlight wiring harness to keep it correct. Has anyone ever tried to replace the entire headlight harness with the car intact? I haven't jumped into it yet, but can I access the harness for removal and reinstallation without removing a bunch of other stuff, such as radiator, headlights, etc? It looks like the harness runs from under the dash all the way to the voltage regulator. Also, I assume that the correct harness would be for a '68 GT car to account for the fog lights?

3) Or, attempt to splice in a new voltage regulator plug and hope that these are the only damaged wires. I know that I can get just the plug.

Thanks in advance for any help!!

BT

'68 Highland Green GT/CS J-code
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Old 04/29/2017, 08:44 AM   #2
franklinair
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I would first attempt to repair/clean the wires & connector at the V/R. Resistance in the wiring should be 0 ohms between the V/R & Alternator.
As a precaution, are you SURE the V/R is OK? (I use the solid state regulators. Don't remember what's on your CS.)
The Alternator wiring harness (NPD P/N 14305-2A, $23.95) connects the main harness to the Alternator (below the Battery tray). The Main harness (that includes the V/R connector is a little pricey (NPD P/N 14290-4B, $203.50) which would also require removing the Instrument cluster to gain access to the in-dash connectors.

Neil

Last edited by franklinair; 04/29/2017 at 09:25 AM..
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Old 04/29/2017, 10:31 AM   #3
TexAg
 
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Thanks, Neil!

I have already cleaned up the connections at the solenoid and the plug to the alternator harness.

I don't believe I can clean up the vr plug. It's in pretty bad shape. I tried to remove the corrosion, but it also looks like it's arced over the years. There's a lot of burning. Plus, I attempted to jump the A to the F, which would bypass the vr, and it doesn't change the output at the battery. I think I would need to splice in a new plug. I may try it because it would be the cheapest and easiest repair. If it doesn't work, I'm only out a a little time and effort, and I can always replace the entire harness later.

Yes, I'm pretty sure the vr is good. I've bought a new one, and have run all of the appropriate test. Plus, when I put a voltmeter on the A post (Bat+) of the vr it's reading 13.4v at idle, which I think is appropriate. So, it appears that the vr is passing the voltage appropriately. The problem is that I'm not getting any voltage at the solenoid.

The harness at the alternator looks good, but I would probably replace it anyway, just to be sure.

I'm more concerned with whether or not I'd be able to remove and reinstall the new headlight harness with the engine bay intact. It seems to run through all kinds of nooks and crannies of the engine bay.

Any other tests that you know to try?

The good news is that I can still drive the car, as long as I plug it in at night.

bt

'68 Highland Green GT/CS J-code
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Old 04/29/2017, 11:36 AM   #4
TexAg
 
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Ok, a little more information. I built a separate harness to bypass the headlight harness.

From the VR:
I - Not used on my car
A - Directly to battery +
S - 12v power source to simulate ignition switch
F - Directly to Field on Alternator
Grounded VR to frame

From alternator
B+ post - Directly to battery +
Ground - To engine ground and battery -
Field - Directly to F on VR

I then took the following readings:
12.58v at battery posts
A and F on VR read 13v+, sometimes up to 15 or 16v.

The strange thing is that no voltage is getting to the battery. This is the same condition with the original harness?

Why would I have 13v to 16v at the A post of the VR, but then a reading on the same wire, 18 inches away only have 12.58v? I used 12 gauge wire for this test, which looks to be the same size as the yellow wire on the VR regulator plug.

When I put it under load, the results where the same, except the reading at the battery was much lower, about 12.3v.

The last strange part is that when I first started the car, the voltage at the battery climbed to about 13.2v, which i would expect, but then stopped and dropped off back to 12.58.

Could this be an alternator issue after all? I've had it tested, and it is showing proper voltage at the VR. Could it be too small? Or maybe it is intermittently faulting?

'68 Highland Green GT/CS J-code
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Old 04/29/2017, 11:44 AM   #5
franklinair
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Do me a favor:
Disconnect the connector for the Alternator harness (below the Battery tray). Inspect/clean the pins & receptacles. Reassemble everything back to the original configuration, and re-check your voltages. I'm particularly concerned about the White wire connection & continuity.

Neil

Last edited by franklinair; 04/29/2017 at 12:31 PM..
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Old 04/29/2017, 12:06 PM   #6
TexAg
 
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I know what you mean. Definitely a knuckle buster.

I also did some Ohm testing. Everything read .01 or lower, so I'm not sure if the wires are even bad. I'll probably do the plug just to make sure I'm not getting some strange leakage at the VR.

Still not sure about the rest of my tests, though.

As always, thanks for your insight.

BTW - had a guy walk up at the GoodGuys rally last month and offer to buy the car. Offer was good, he wanted to do a partial trade on a '68 S-Code fastback. But I just couldn't bear to part with the CS. Thought you would like to know that others appreciate your work as much as we do!!

bt

'68 Highland Green GT/CS J-code
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Old 04/30/2017, 02:33 PM   #7
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Keep in mind that what I'm about to say is speaking generally, because I don't have a car in front of me for reference. If you're getting 14-16 volts from the alternator, your alternator is working correctly. I believe the reason you're not getting full voltage at the battery is because of a partially broken wire from the regulator to the battery. You mentioned burned wiring and signs of arcing. This is causing a resistance in the wire and a voltage drop. If you were to measure the resistance with a digital meter, it would probably still show near 0 resistance because of the high impedance of the meter. Only when your current flows would it show, which is why your voltage reads low. If you have an old analog meter, it will give a more accurate reading in this case. If you try to cut out the old harness section and splice in a new one, you'll probably have new issues based on the method of splicing you use. If you use crimp connectors, you won't get full electrical contact with all conductors, the crimp will eventually loosen, and you can get water into the joint, causing corrosion. More trouble down the road. If you try and solder 50 year old oxidized wiring, you won't get a really good joint and the larger wire will act as a heat sink, making it almost impossible to get the solder to stick without using a torch. Both methods change the resistance of the wire run, which will affect your ammeter (useless as it is) because both connections are in the area you're working on. My recommendation, painful as it may be, is replace the harness with a good quality new one, unless you're really talented at wiring repair.

Steve

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Old 05/01/2017, 04:27 PM   #8
TexAg
 
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Thanks, gang.

Neil - That was my first action. All of the connections have been cleaned and put back together. No change.

Steve - I did a lot more research, and I think you are correct. It does appear to be a resistance issue. Good points about splicing the harness. I'm going to do a couple more voltage drop tests to see if I can isolate the problem, but I'll probably just go ahead and replace the entire headlight harness, assuming that's the problem. If nothing else, at least I'll have a brand new charging system.

I did have the alternator tested while it was in the car, but I think I'm going to pull it and put it on a machine in order to isolate the alternator itself.

'68 Highland Green GT/CS J-code
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