1968 tail light problem

[flame_thrower]

Right tail light does not work. Tail light works when headlights are on though. Light does not work with brake.

Also, when using right turn signal it activates right front signal light and left rear signal. Very weird.

Left turn signal activates left front and rear light.

Anybody know what is going on here?

[ole dollor]

sounds like some one has crossed the turn signal wires on the rear , did they work right before ,how long have you had the truck, also clean all bulb sockets and all grounds, check your wiring at the back wiring harness. make sure your tail light assembles are grounded good also. also check your bulbs, some times the filament will cross over inside the bulb, this should give you a place to start looking for the problem...good luck.

[LockDoc]

Just to expand on what ole dollor said.

I'm betting on a bad ground circuit. I would remove all of the ground wires in the rear, clean and re-attach. I would also run a ground strap from the frame to the bed, making sure all connection points are clean metal. Ground strap from engine to frame also.

Like ole dollor said, clean the bulb sockets and contacts and also unplug and check the connector where it goes through the rear cross member.

Some things to check out.

LockDoc

[Shyguy]

All great advice. Eventually you may trace the problem down to the turn signal switch. That is what is wrong with my truck, but try all the other advice first before you worry about the switch.

[daveo68]

Had a similar problem on my '68. Worked on it for three days,found bad ground on one of the tail light assemblies. Can be anywhere,though.

[flame_thrower]

Switched bulbs. Didn't work. Pulled out light assembly, cleaned. No change. Wiring harness seems ok, but I will continue to look for maybe bad ground or wire to metal touching. Wonder if it's not in the turn signal switch or somewhere in the steering column. Noticed a while back that brake lights didn't work at all. I switched from low to high back to low beam on the floor switch and that fixed the problem. I did have a tag light installed and they tied the wires to the wiring harness. Possible problem?

[ole dollor]

you might want to check the connection at the fire wall, make sure its clean and plugged in good, also if you lose your brake lights and everything else is working it will be your turn signal switch in the steering column . it really sounds like you have some major grounding problems, but you may just have some wiring problems.

it is possible that when they wired up the tag light they may have pulled the harness apart a little.follow it to where it plugs in on the left rear of the frame .

[VetteVet]

Originally Posted by flame_thrower

Right tail light does not work. Tail light works when headlights are on though. Light does not work with brake.

Also, when using right turn signal it activates right front signal light and left rear signal. Very weird.

Left turn signal activates left front and rear light.

Anybody know what is going on here?

Your problem is the right light is not grounded to the frame and is finding its ground through the other lights when the headlight switch is on.

The right brake light in the same socket is is using the ground through the left signal light and lighting the left signal but not the right.

The tail lights do not go through the turn signal switch but they use the same fuse as the brakes and turn lights.
Get a good ground on the right brake/turn socket and it should fix your issues.

[daveo68]

That is what was wrong with mine, not a bad ground, the ground was off the screw on the tail light assembly. Was just on by a strand of wire.

[kwmech]

Do you have a trailer plug? AND the fuse is not the same as the turn and brake, it is the same as the dash lamps

[domeier]

If'n I wuz you, I'd start troubleshooting at the turn signal switch and work my way out from there.

Purple in, is power from the turn signal flasher relay
Black/White in, is power from the stop lamp switch
Brown in, is power from the hazard flasher relay
All grounds are made after the lamp elements
Turn indicators in dash are powered off the front turn lamps

Left turn:
Purple in to switch goes to Black/yellow out (left brake/turn lamp)
Purple in to switch goes to Black/Blue out (left front turn lamp)
Black/White in to switch goes to Green out (right brake/turn lamp)

Right turn:
Purple in to switch goes to Green out (right brake/turn lamp)
Purple in to switch goes to Blue out (right front turn lamp)
Black/White in to switch goes to Black Yellow out (left brake/turn lamp)

No turn:
Black/White in to switch goes to Black/Yellow out (left brake/turn lamp)
Black/White in to switch goes to Green out (right brake/turn lamp)

I just went through something similar to your problem, and it took me a little while to finger out how the switch is supposed to work. Because the turn and brake lamp elements are shared, the switch is a bit complex. My switch was shot. Only lasted 42 years...

[domeier]

ps: The running lights (rear tail lights and front running lights) are not at all connected to the brake/turn/hazard circuits. If the running lights work or not, they have nothing to do with brake/turn/hazard.

Oh, and pps: Good luck!

[Shyguy]

Originally Posted by domeier

If'n I wuz you, I'd start troubleshooting at the turn signal switch and work my way out from there.

Purple in, is power from the turn signal flasher relay
Black/White in, is power from the stop lamp switch
Brown in, is power from the hazard flasher relay
All grounds are made after the lamp elements
Turn indicators in dash are powered off the front turn lamps

Left turn:
Purple in to switch goes to Black/yellow out (left brake/turn lamp)
Purple in to switch goes to Black/Blue out (left front turn lamp)
Black/White in to switch goes to Green out (right brake/turn lamp)

Right turn:
Purple in to switch goes to Green out (right brake/turn lamp)
Purple in to switch goes to Blue out (right front turn lamp)
Black/White in to switch goes to Black Yellow out (left brake/turn lamp)

No turn:
Black/White in to switch goes to Black/Yellow out (left brake/turn lamp)
Black/White in to switch goes to Green out (right brake/turn lamp)

I just went through something similar to your problem, and it took me a little while to finger out how the switch is supposed to work. Because the turn and brake lamp elements are shared, the switch is a bit complex. My switch was shot. Only lasted 42 years...

Thank you for posting this, it will help me fix the turn signal/brake light problem I have with the '67 swb stepper.