Taillights not working, brake lights work when headlights are off?

DATURNERS

MEMBER
2005 FORD F-150
5.4L
V8
4WD
AUTOMATIC
150,000 MILES

Hello,

Hoping someone will be kind enough to help me with chasing electrical ghosts. I think it might be the brake switch, but I'm not 100% sure. I have checked fuses and bulbs but did not test connections with a circuit tester.

Headlights, running lights and front flashers work.

Taillights don't come on at all, rear flashers work but dim, and brake lights only come on if headlights are off.

The part that throws me through a loop is, the flashers speed up when the brake is engaged.

I do hear the brake switch click when the headlights are off, but do not hear the brake switch click when the headlights are on.

Thank you in advance.

1 Reply

KEN L

MASTER CERTIFIED MECHANIC
42,940 POSTS

This sounds like a ground issue I would check at the rear of the truck because that is the problem most of the time. here are to guides to help you and the taillight wiring diagrams so you can see how the system works and where the grounds are located.

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

and

https://www.2carpros.com/articles/turn-signals-not-working-blinker

Check out the images (below). Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.

Images (Click to make bigger)