Tail Light Issues

[oldcurmudgeon]

1970 318/auto Dart Swinger standard dash/cluster

I'm having some tail light problems and I'm not sure if it's tied into the signal switch, the flasher, headlamp switch or none of the above. I'll try to give as much detail as I can. When I mention "tail filament" I'm referring to the tail light and not the brake/signal light.

Left signal on with headlights on:
Left tail filament stays lit.
Left signal/brake filament blinks brightly on and off.
Right tail filament barely glows.

Right signal on with headlights on:
Left tail filament normal
Right Tail filament blinks dimly
Right signal/brake filament does nothing

Brakes on with headlights on:
Left- both filaments on normal
Right- all off

Brakes on with headlights off:
Left- Brake/signal filament bright
Right- only tail filament glows dimly

Headlights on only:
Left tail filament normal
Right tail filament about 2/3 as bright as left

Emergency Flashers on:
Front normal but fast
Rear nothing on either side

Headlights:
Testing with plugs unplugged in trunk
Left black tail light wire: 11.7v
Right black tail light wire: 11.7v

Brakes on:
Trunk Left green wire- 11.7v
Trunk Right brown wire- 0v
Green wire at turn signal switch under-dash column plug- 11.7v
Brown wire at turn signal switch under-dash column plug- 0v

The right stop/signal filament does not light or show voltage under any conditions.

That's as far as I've gone so far. I also changed out the right rear lamp. The wiring is all non-molested.

Thanks for any ideas.

 

[67Dart273]

I would say you have two problems

1--Right socket is not grounded. This explains some of that action

2--I think you have a bad signal switch

Before condemming it, move up to the kick panel connector for the rear harness, and back probe the connector under various conditions for joltage.

If you show passable (11.5, etc is low but passable for this test) voltage, at the tail terminal, and at left/ right with the brake pedal depressed, and voltage, flashing or not, in left or right turn, you can look to harness/ socket problems

Here's how an ungrounded socket works. Let's say you have a completely normal system, and all you do is unground the socket.

With head/ tail lights off, and you either apply brakes or signal, the juice goes through the signal filament, and cannot get to ground, so it goes "in series" through the (unpowered) tail filament, and because all the rest of the park/ tail/ marker lamps on the car are also unpowered (but grounded) the "other end" of the tail filament now feeds power to all the rest of the bulbs, and through those filaments to ground.

So the bulb lights, somewhat dimly.

If you simply turn on the park/ head lights, NOW you have tail light power on the tail light filament, so ungrounded socket "bulb" goes out.

This is because you have +12 on one side of the signal filament, through the filament, through the tail filament, and +12 on the other end of the tail filament --no current flow.

With tail/ head "on" and no brakes or signal applied, the path is reversed. In this case, the only thing "to ground" is the other rear signal, because with the signal lever centered, both rear lamps are connected together to function as brake lamps.

So now power comes to the tail filament, through the filament, through that bulb's signal filament, up front to the signal switch, through the switch to the opposite side wire, back to the rear to the opposite side signal filament, through that filament, and finally to ground.

The REALLY interesting cars used to be the 60's Chevys, which had some of the lamps in the quarters, on some in the trunk LID. You really had to 'pay tenntion" to get everything properly grounded, and it used to be comedic funny to see how many of those "weren't working"

 

['74 Sport]

The first thing I would do is check all the ground wires. Clean all terminals of any oxidation. Push the ground plugs on-off-on-off a few times to ensure good connections. Check inside all of the bulb sockets to make sure the terminals are clean, too. Use the pink eraser end of a pencil and scuff them a bit to remove potential oxidation. The rubber (not vinyl) erasers are slightly abrasive, but won't harm. Apply some dielectric bulb grease to the metal components of the sockets.

 

[oldcurmudgeon]

THANK YOU!!

As soon as I read your responses I slapped my head. Bad grounds- Of course!

I clipped a jumper to the bumper and then touched the lamp socket with the right signal on. The tail light filament was flashing dimly and as soon as I made contact it stopped and the stop/signal filament started flashing brightly. Next I touched the jumper between the tail light housing and the socket and once again the filaments switched.

I started by pulling the housing to bumper bolts which had very rusty heads and washers. I cleaned up both just to eliminate any problems there.

The socket looked fine where it was pressed to the housing but I still carefully and slightly pried up one section of the socket rim and scraped underneath it. I tapped it back down and it works great now. My right tail light is now as bright as the left, I have a right signal light and a right brake light.

The emergency flashers still do not work in the back but at least everything else is working now. I'll look at them over the weekend.

Thanks to both of you. I love relatively simple fixes!

 

['74 Sport]

I like simple fixes, too; however, electrical issues tend to be the most bothersome for me. Glad to help.