Headlight/ Electrical problem 71 Road Runner. HELP

Posted By: shamefulcuda

Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 03:15 AM

Man this 71 runner is kickin my a**. I got the car going today and trying to iron out the kinks and what I ran into today has baffled me. When I turned the headlights on, they were flickering along with taillights to the tune of the idle. When I revved the car up all the lights blew (dash lights, taillights, and headlights). Fuses didnt even blow. Also noticed the alternator not charging according to my volt meter, as I had originally thought maybe the voltage regulator was bad. But with the alternator not charging I dont see how it could be that. I have 12.2 volts at the battery. Engine bay has a new wiring harness. I am almost certain its not at the bulkhead and its under the dash. I have spent the better part of 8 hours today reading schematics and tracing things down. I have no idea at this point of what it could be. Any ideas? Please help Im ready to give up. Also the car has to be in the run position for the lights to work. I know that is wrong as well as it should be on battery power. It feels like i have tried everything. The wiring underneath doesnt look abnormally butchered. There is a couple of splices but nothing crazy.

Posted By: buildanother

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 03:29 AM

Wiring and/or alternator problem. The alt has to charge to blow things out.

Posted By: MoparMarq

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 03:43 AM

Without looking at the schematic here, first thing I'd do is fix the lights-only-on-with-ignition-switch-in-run thing going on. Some splice in there may be providing some funky feedback to the voltage regulator. Perhaps a splice in there is causing the power use by the lights to drop the voltage to the positive side of the voltage regulator, making it "think" that it needs to up output from the alternator.

Posted By: shamefulcuda

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 04:03 AM

I would love to fix the problem with the lights coming on only in run, except I have no idea at this point. I realize wiring problem somewhere but keep in mind, I have been up and down this harness now, and Im not seeing any added splice. I have found 2 splices but wire was put back (in other words looks like it was broke and properly repaired). So nothing has been added in the harness. The engine bay harness is new. I will keep at it tomorrow, was hoping someone has encountered this. From what I can tell checking alt , it is not charging the car.

Posted By: Sinitro

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 04:14 AM

Quote:

Wiring and/or alternator problem. The alt has to charge to blow things out.

Sounds like the alternator threw out a very high voltage such as 18V if the regulator or something internal shorted for a split second driving it up. Note that fuses typically blow on current overload not voltage overload..

Just my $0.02...

Posted By: shamefulcuda

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 04:40 AM

I thought about the high voltage and so what I did is disconnected the bulkhead connector (1st plug in closest to master cylinder) to sort of eliminate the alt and charging system and that didnt change a thing. Rear taillights were still flickering with the idle of the car. I didnt dare rev it up as I didnt want to burn another set of bulbs (they arent cheap anymore)

Posted By: MoparMarq

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 05:49 AM

Quote:

I would love to fix the problem with the lights coming on only in run, except I have no idea at this point. I realize wiring problem somewhere but keep in mind, I have been up and down this harness now, and Im not seeing any added splice. I have found 2 splices but wire was put back (in other words looks like it was broke and properly repaired).

It may look to be properly repaired, but looks can be deceiving. I hope you have a FSM to follow along on the schematic. My FSM is '72, so may be a little different. The feed to the HL switch is 12 gauge black to terminal on switch labelled B1. If, for whatever reason by PO, it was cut or replaced to be supplied only in run (maybe they ran down the battery for some reason), he might have used a dark blue ignition feed wire from somewhere in the harness to replace the black feed for the HL switch. If so, that would explain the on-only-in-run phenomenon, and explain the flicker at idle due to no charge from alternator and nature of power use by coil.
Additionally, if the dark blue wire he used was the one that goes out to terminal 23 on the bulkhead connector, that MIGHT explain why the VR gets low power and therefore doesn't allow the alternator to charge, even though the harness on the engine side of the bulkhead connector is new and in perfect shape.

Quote:

So nothing has been added in the harness. The engine bay harness is new. I will keep at it tomorrow, was hoping someone has encountered this. From what I can tell checking alt , it is not charging the car.

I may be out in left field here with what I described above, but a few things can be checked pretty easily. I assume the car runs fine without the lights on (except for the charging issue). With the car not running, but the key in "run", see if there is power to the blue wire on the electronic VR harness. There should be, if the car runs. If not, something is goofy with the new harness, and I'm at a loss. The problem is probably in the cabin side of the dash harness with the hot (black wire) factory splices and ignition feed (blue wire) factory splices. Maybe one of the black wire splices went bad at some point with the PO, and he pulled power for the HL switch from whatever he found that had power with the key on.

I'm really curious about what you find with this. I've never heard of it before. Good luck.
-Marq

Posted By: shamefulcuda

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 06:05 AM

Thanks, I will try some more tomorrow and this weekend. Yes the car runs fantastic otherwise. Im using a Service manual for schematics, so im good there. What does PO mean? Drawing a blank on that.

Posted By: MoparMarq

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 06:15 AM

Quote:

I thought about the high voltage and so what I did is disconnected the bulkhead connector (1st plug in closest to master cylinder) to sort of eliminate the alt and charging system and that didnt change a thing. Rear taillights were still flickering with the idle of the car. I didnt dare rev it up as I didnt want to burn another set of bulbs (they arent cheap anymore)

'71 must really be different than '72, 'cuz if that connector is disconnected on a '72, it won't run (no power to VR or ignition coil). If the harnesses are the same between years, or nearly so, you've got something weird going on if your car still runs with the harness disconnected...

I'm really at a loss to figure it now...

Posted By: MoparMarq

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 06:17 AM

Quote:

What does PO mean? Drawing a blank on that.

PO = previous owner

OP = original poster

Posted By: shamefulcuda

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 06:29 AM

I jumped the solenoid with that connector off to start it. Did not use key.

Posted By: Yancy Derringer

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 08:39 AM

It's too darn late tonight to think clearly, but I think you have a problem in the bulkhead/ ammeter/ underdash in harness splice."

I believe that a wiring fault has disconnected the battery from the alternator feed so that the lights are drawing power from the alternator, but the alternator is not connected to the battery. Check carefully in that area

If that splice has broken loose in the harness, it's possible that part of the conductors are connected to the alternator feed, and part of them are connected to the battery

For example, my '70 book shows that the black wire from the ammeter AND the feeder for the headlight switch both terminate at that splice. I'd be considering untaping the black ammeter wire until you find that splice

I posted this out of my 67 manual because it's pdf

If you find the ammeter to the far right, note "R6A-12BK" at the bottom of the alternator and trace it back, where all that stuff comes together is a big splice "in harness."

Now notice that L1-16-BK takes off to the lower right of the splice, and runs right down to the headlight switch. THIS IS the main feed that runs the lights.

If somehow, that splice came apart in such a way that some of the car was "being fed" power and other parts were not, this could explain what's goin' on.

(In my lifetime, I've found three cars that had one of those spliced fail. First one, I remember, was a buddies 68 Roadrunner--the ammeter would dance all over hell. We were sitting in the car in a driving rainstorm, the harness and dash all over our laps. I found it and fixed it, and he just could not believe it.)

Posted By: jbc426

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 09:40 AM

Why don't you start by putting a volt meter on the alternator and see whats going on there. Measure with the car off, with it idleing and s-l-o-w-l-y bring up the rpm's. It shouldn't go any higher than 14.4 volts.

Posted By: CYACOP

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 12:38 PM

Headlight switch could be bad

Posted By: Yancy Derringer

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/03/10 06:28 PM

Quote:

Why don't you start by putting a volt meter on the alternator and see whats going on there. Measure with the car off, with it idleing and s-l-o-w-l-y bring up the rpm's. It shouldn't go any higher than 14.4 volts.

This won't work if there's some sort of wiring problem that separates the battery. The regulator sense may well be operating from the battery, and so the regulator "thinks" the voltage is low, and has the field ramped up trying to charge the battery

(We used to run into this with those %%%%%% diode battery isolators when they failed. They would charge the heck out of the auxiliary battery, but the main would be going dead. There's been at least one boat had a bilge explosion because of them)

Posted By: jbc426

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/04/10 12:22 AM

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Quote:

Why don't you start by putting a volt meter on the alternator and see whats going on there. Measure with the car off, with it idleing and s-l-o-w-l-y bring up the rpm's. It shouldn't go any higher than 14.4 volts.

This won't work if there's some sort of wiring problem that separates the battery. The regulator sense may well be operating from the battery, and so the regulator "thinks" the voltage is low, and has the field ramped up trying to charge the battery

(We used to run into this with those %%%%%% diode battery isolators when they failed. They would charge the heck out of the auxiliary battery, but the main would be going dead. There's been at least one boat had a bilge explosion because of them)

It will tell him the voltage at the alternator to start with. There's a whole series of test that need to take place in a systematic fashion, but first things first.

Posted By: Yancy Derringer

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/04/10 12:49 AM

I know exactly what you said, what I'm saying is, IF IF IF IF the problem is something on the wiring as I described, THE ALTERNATOR VOLTAGE WILL BE IRRELEVANT and may in fact be "very high."

READ IT AGAIN. If a wiring fault has disconnected the alternator output from the battery, and left the voltage supply to the regulator IGN terminal going to the battery, then the regulator will "think" the battery is low (which it WILL be) and will ramp up the field current, causing a HIGH voltage condition at the alternator output. IT WILL NOT BE nominal 13.5-14.5 V, it WILL BE in fact much higher and CAN in fact cause this very problem.

Posted By: MoparMarq

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/04/10 02:39 AM

Quote:

I know exactly what you said, what I'm saying is, IF IF IF IF the problem is something on the wiring as I described, THE ALTERNATOR VOLTAGE WILL BE IRRELEVANT and may in fact be "very high."

READ IT AGAIN. If a wiring fault has disconnected the alternator output from the battery, and left the voltage supply to the regulator IGN terminal going to the battery, then the regulator will "think" the battery is low (which it WILL be) and will ramp up the field current, causing a HIGH voltage condition at the alternator output. IT WILL NOT BE nominal 13.5-14.5 V, it WILL BE in fact much higher and CAN in fact cause this very problem.

I go with this analysis also. It may be in the splice indicated above, OR, looking at the schematic for '72, he may get lucky. I believe it could be just on the inside of the bulkhead connector on terminal 18 where the alternator output comes through the bulkhead connector to feed that splice. It's possible that pushing the new harness on from the engine side pushed the terminal out of the bulkhead connector on the cabin side. If so, it'd be relatively easy to replace the terminal with one from an electrical parts store with the proper barb on it to retain it in the bulkhead connector sleeve location.

Posted By: jbc426

Re: Headlight/ Electrical problem 71 Road Runner. HELP - 12/04/10 08:13 AM

I understand what your saying, and it could be that or a bunch of other things. I just like leaving all the if's, the maybe's, the might be's out of it and begin with a logical series of tests to see what is actually going on. Testing and troubleshooting have always served me well.

Posted By: shamefulcuda

Re: Headlight/ Electrical problem 71 Road RunnerUPDATE - 12/06/10 11:39 PM

Sorry guys I had a wisdom tooth pulled on friday and I just got back out there to mess with it again. Anyhow , I have no charging at the battery. I have about 44-48volt output at the altenator. At the ballast resistor with car running i have 16-18volts which tells me the volt regulator is working but still putting out to much voltage. I still have no idea at this point, but this is where I am at today. I kind of just started a few minutes ago and did some quick checks. Alt is hooked up correctly, wiring in engine bay is new so looks fine. I will check the bulk head again I guess. Thanks for continuing to help!

Posted By: shamefulcuda

Re: Headlight/ Electrical problem 71 Road RunnerUPDATE - 12/07/10 12:12 AM

BAM! 15 mins later I found the problem. A wire in that splice where Q3-12R, J1-12R, R6A-12BK and L1-12BK all meet up was not connected. Fixed that splice and were all good and 13.2 at the battery, 13.8 at alt and all lights stayed lit and are not flickering! 35 bucks worth of bulbs later

Posted By: Yancy Derringer

Re: Headlight/ Electrical problem 71 Road RunnerUPDATE - 12/07/10 02:56 AM

Quote:

BAM! 15 mins later I found the problem. A wire in that splice where Q3-12R, J1-12R, R6A-12BK and L1-12BK all meet up was not connected. Fixed that splice and were all good and 13.2 at the battery, 13.8 at alt and all lights stayed lit and are not flickering! 35 bucks worth of bulbs later

WAY ta go!! I've found a similar "in harness" problem on 2-3 cars "back then"

Posted By: jbc426

Re: Headlight/ Electrical problem 71 Road RunnerUPDATE - 12/07/10 03:20 PM

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BAM! 15 mins later I found the problem. A wire in that splice where Q3-12R, J1-12R, R6A-12BK and L1-12BK all meet up was not connected. Fixed that splice and were all good and 13.2 at the battery, 13.8 at alt and all lights stayed lit and are not flickering! 35 bucks worth of bulbs later

WAY ta go!! I've found a similar "in harness" problem on 2-3 cars "back then"

Good call Yancy!