1968 coupe, rear lights not working right

[Falcon79]

Does anyone have any clue as to what might be wrong here?

Here are the symptoms-

When headlights are off:
the blinkers work, but not that bright
brake lights do not work
reverse lights work

When the headlights are on:
the blinkers do not work
brake lights do not work
running lights work
reverse lights work

The rear harness is brand new, I checked the ground that is attached to the trunk support and it is on bare metal. All the lights work up front the way they are supposed to, all problems are in the rear.

 

[WTFO]

Do you have the right amperage fuses in the correct spots in the fuse box? Double check the adjustment of the brake light switch at the pedal. Did you change the flasher unit out?

 

[Falcon79]

I'm pretty sure the fuses are right, I'll check though. I'll also take another look at the brake light switch. I didn't change the flasher unit out, I figured since the front lights are flashing correctly then that couldn't be the problem.

Thanks for the response.

 

[robbz28]

Check the grounds to the front lights as well, I had an issue with my lights being screwy like that and It actually ended up being my front light harness not being grounded properly. Also sounds like you may have the running light and the brake light wired up backwards.

 

[Falcon79]

Well I checked the wiring harness for the rear lights and it is plugged in correctly. I also replaced all fuses. The weird thing is that when the headlights are on, you see the taillights blinking, its very very faint but they are blinking, its like whatever causes the blink to be brighter than the running light is failing. Just to be sure I ordered a new flasher module and a new brake light switch.

 

[WTFO]

Your still running the external voltage regulator right? Double check that ground wire that should be on one of the screws on the radiator support panel. Like RobbZ28 said- it could be related to the front lights as well since all the lights are related to the headlight switch and the flasher unit in the fuse box. Keep us updated and good luck!

 

[Falcon79]

I solved the problem. It turns out the after market sockets that you plug the taillight bulb into are total crap. They were not lining up right to make a good connection to the bulb. I cut them out then spliced in the originals from the old harness. Everything worked perfectly! I'm going to tune the carb then take it down to get inspected this week!At least I know everything is grounded and all my fuses and switches are working, lol.

Thanks for all the help!