Tail Light Wiring Help Needed

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zigman

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Hi guys,
I am a fairly new owner of a 72 Dart and I am having some issues with my tail lights. I have 3 wires that connect with the rear tail assemblies, a violet (goes back up light) and a brown and black which go to the tail/brake/turn light (1157 bulb). I get power to the brown wire when the brakes are pressed and when the blinker is on. That seems correct to me. However, when I turn the headlights on, I get power to both the black and brown (without the brake depressed or blinker on). This does not seem right to me. It seems to me that I should only be getting power to the black when the headlights lights are on. According to my wiring diagram, the black connects with the side marker lights. However, I am puzzled why I am getting power to the brown when the head lights are on. Any advice would be appreciated.
 
Grounds, grounds grounds.:D
I use a separate wire clipped to the bumper or a body bolt to check them, and touch the bare end to the bulb base where it goes into the socket while the light is on.
Grounds in the tail/brake lights area suck on these cars, and I'd bet you have some crossflow of power due to bad grounds.
I actually drilled the housings and ran a dedicated ground through the lens housings to the bulb sockets themselves because they were so sketchy about it.
Note that even if you have a for sure ground to the light assy, the actual bulb socket metal looses it's ground to the metal housing from corrosion between the two metals.

Went through that same thing not only on my 73 but the Wife's 72 as well.
Pretty much with ANY electrical problem on these cars check grounds first and you'll usually find that was the problem.
 
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I believe you may have a bad ground. Are you testing with the all sockets installed?
 
Thanks for the responses. I was wondering if it might be a ground issue myself, but I traced the brown and black wires all the way up to where they connect behind the drivers side kick panel and I am getting power to both wires up there when the headlights are on. Therefore, it seems to me that it probably is not a grounding issue....although perhaps I am wrong about that? Electronics is not my strong suit. Perhaps I will try a dedicated ground wire back on the bulb socket as TrailBeast suggested and see if that makes a difference. Thanks again for the suggestions!
 
You may have a bulb with the filaments shorted together, or even something wrong in a socket. I would start by:

Pull the kick panel connector loose, this will isolate the rear harness, and pull ou the rear lamp bulbs

"What you have" now is the tail light wire should go to both rear lamps, and the two turn/ brake conductors should be isolated. This means that if you put an ohmeter into the two socket terminals of each rear socket they should show open, as well as open to ground.

If the above checks out, leave the kick panel connector off, look up in your manual for the wire color/ pinouts to the that connector, and check that it has voltage at and when it should. IE tail lights on should power the tail circuit. The dome light circuit will be hot all the time. The turn / stop wires should only be hot when the brake pedal is pressed, or one at a time when the turn sig switch is operated with key "on"
 
If the bulb sockets aren't grounded the current will follow the other circuit and show up anywhere you check for it. If you were at the front 1157 fixtures park lamp current would turn the turn indicators in the inst' panel on. anyway... Ground the sockets, issue solved.
 
Yep, you guys nailed it. A bad ground was causing the current follow up the brake/turn signal lead when I turned the lights on. I ran a new dedicated ground wire to each bulb socket and now things are working correctly. I would not have figured that out on my own. Thanks for the help and happy new year!
 
Consider the double filament bulb as 'M', center point being ground, upper 2 points as elements. The current didn't ground so it continued traveling seeking ground. The front park circuit would find a ground at the turn indicators and/or fender mounted fixtures. If you had first removed the 'M' bulbs and then went inside the car looking for a fault... No fault found. That proves the fault to be at bulbs and sockets. We immediately suggest fault at socket ground because its where both circuit come together, middle of the 'M', and because we've seen it many times before.
 
How are you guys grounding the bulb sockets for the tail lights? Soldring wire to it and grounding to the chassis somewhere?
 
My 72 duster, I was getting some funky stuff other day ( auto pro electrical talk) concerning the tail lites, I found the factory 4 way splice in trunk where the 2 tail lite and 2 running light wires were simple needing taking apart and cleaning and redoing. Beengood since! ( fingers crossed).
 
dieselman966 said:
How are you guys grounding the bulb sockets for the tail lights? Soldring wire to it and grounding to the chassis somewhere?
Click to expand...

This is a good way. For those of us who remember "stuff" like the 60's Chevys with the lamps mounted IN THE TRUNK LID, grounds were always an "interesting issue"

My 70RR, in which the sockets just "clipped" out of the housings from in the trunk, had separate ground wires attached to each socket (There were 4)

My 63, Circa 1970, "newly stationed" at NAS Miramar

Hams_011.jpg
 
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