My tail lights don't work.

The blinkers work. And the brake lights work when the lights are off, but as soon as I turn the lights on the brake lights don't work anymore.

I checked the wires with a test light and there is power to the socket when the lights are on. However the bulb does not light up and the brake lights don't work even though there is power in the wires like their should be.

Can anyone help me understand why the wires have power like they should and the brake lights work but the tail lights don't work and when I turn the tail lights on the brake lights don't work?

Thanks for the help!!

 

Maybe a ground issue. Sometimes a bad ground can makes lites do some really weird things.

 

There is a ground on the driver side between the rear bumper and the rear tire it's on the frame. If I remember right there's also one In the passenger side tail light housing I think the wires brown? Good luck

 

No, not brown!!!! All lighting-system ground wires are black... the brown is positive (power) for the tail lights, front side marker lights, front parking lights, cab-mounted roof lights (if installed), rear license plate illumination. Grounding the brown wire will blow a fuse....

 

Regardless of that, yes, look at your grounds... weird things can happen with bulbs when one of the grounds is missing and the electricity flows through other portions of the circuit in search of a ground. Another thing that can really weird things out is when one of the filaments in a dual-circuit bulb breaks off its conductor and falls onto the adjacent conductor inside the bulb. The rear tail/brake lights use such a dual-filament, dual-circuit bulb... so do the front parking/turn lights.

The brake lights and turn signals share the same circuitry and all come together in the turn signal switch but your problem involves the parking lights, that circuit never touches the turn signal switch so that device can't be causing the problem.

What comes to mind as a possibility is the headlight switch... there is a tan (I think with a white stripe) wire in that mass of wires there that is known to overheat and melt not only its own insulation but that of adjacent wires, this creates short circuits and all kinds of weird stuff can happen.

In sum, you are going to need to do some serious diagnosis of your lighting system but start with the easy stuff... dual-filament bulbs (are they installed correctly? they're meant to go in only one way but people sometimes force them the wrong way), grounds, various connections and such....

Also, user-added trailer wiring harnesses are really known to cause these kinds of problems as many users use poor wiring techniques when doing their own wiring....

 

Oops sorry

 

Many times the ground part of the socket goes bad inside the socket.
Try the test light grounded to the ground side of the socket

 

It's the ground. The brake/turns don't have a ground, so they are using the running light circuit as a ground. That's why when the headlights are on(runnngs are on also) the brake lights don't work because there is voltage on the running light circuit and it blocks the ground that the brake lights are trying to use.

 

Thank you for all the replies.

It is currently getting a new gas tank put in it but when it gets back I will try to ground those tail lights and see if that is the problem.

Thanks for all the help. I'll keep you updated!

 

Welcome to the forum, stuckstudent!

 

Same issue I am having with tail lights not working, but turns, hazards, brake lights, and reverse lights do work.
I have read several threads and this makes the most sense. Hopefully, I can track it down in daylight.
I will update when/if it works. I started in the fuse boxes and no luck there.

 

What is your issue exactly? If you have a grounding problem, your tailights will work with the brake lights off.

 

 

On mine it was a ground issue. I ended up running a ground wire along the frame to a point where I knew I had a good ground. Once I had a good ground, the problem went away.

 

Old thread, but want to post my findings for no taillights on my 2012 Ford F-250, the yellow wire on the taillight plug was corroded, plug was located under box near the Left taillight