Tail Lights Working Intermittently?

So I’ve got a weird one.

First I noticed my left tail light was out when braking with my headlights off.
Then, next day left was working fine but the right was out when braking with lights off.
THEN next day, both were out when braking with lights off.

Next morning, right was out with my headlights on. When I got home from work, left was out with headlights on.

Waited a couple of days because I’m lazy, and when I went to replace the lights this happened....
Right was out when I went to work, then working when I got home. When I got home, left was out.
Pulled the bulb and put it back in. Both are working fine now with the headlights on. Haven’t tested again with the headlights off.

I just put in an AUX fuse block and used the factory battery ground, could this be the culprit?

 

Aaaand I just checked. No brake lights with the headlights off.

 

It was working correctly.
You modified something (Aux Fuse Block).
Now it doesn't work correctly.

If it were me I would do the obvious action and Undo what I did and see where it stands from that point.

 

Does the brake light ground use the factory battery ground though? Lot of people setup an AUX fuse block and use the factory ground. I guess I’ll check that ground in the morning....

 

A ground is a common point going back to the negative terminal on the battery. Yes, the brake lights have a ground wire. All electrical components have a ground wire path back to the battery.

As I said before: I would undo everything I did before the brake lights started screwing up. Then see what happens then if it goes away then you know what caused it. If it doesn't you can continue troubleshooting from that point.

If you have a meter or test lamp you can check for voltage at the brake light socket when it isn't working. If you have voltage and a good lamp and it still doesn't come on you have an open ground connection.

 

The tail lights not working as well as the brake lights not working on both sides, indicate an issue with a ground which is common to both lamp circuits in the taillight as well as from passenger and driver side.

check to see if your license plate lamps are also affected, as that shares ground at connector BD by the rear differential. Chances are, if you did something with the electrical system and now there’s an issue, it was something you did and as @Jimmyh suggested, go undo that. There are very few coincidences when it comes to these issues.




Here is the medical equivalent to your issue.

 

Welp, after all the troubleshooting it looks like I’m an idiot. The bulbs were loose..... guess that’s what happens with aftermarket bulbs.

 

Well live and learn. Thanks for getting back with the answer for what you found.

Look at it this way, Your reply could prevent someone else from making the same mistake...