Tom Werner

I have a 2004 F150 with a 4.6l engine.

The Third brake light does not work, and the brake lights for a trailer I use on occasion do not work (all other lights on trailer work, including turn signals).

I checked the power coming out of the trailer light connection on the truck, and nothing when the brakes are depressed.

Can I assume that I have one problem (meaning power is not supplied to either the high mount stop light and the trailer light connection), or do I have two separate issues?

Any chance there is a separate fuse for the Third Brake Light?

Anyone solved a similar problem? If so, how?

Thanks,

Tom

techrep

iTrader: (1)

Have you checked fuses ? And I assume your cruise control don’t work either..

Tom Werner

Third Brake Light was fixed with a new bulb, even though old bulb looked fine. Cruise control has and continues to work fine. Fuse box placement is idiotic. It's just the worst.

Trailer lights now seem even more screwy than before. I attached the plug with the trailer unattached, and no lights are working now (previously running lights and turn signals worked). Does the trailer need to establish ground through the hitch in order for the lights to work? Doesn't seem like this should be the case, since one of the 4 connections for trailer lights is ground.

Looks like I need to do some more troubleshooting with my multimeter...

Tom

techrep

iTrader: (1)

No.. they will work without being connected

redfishtd

Start by bringing a ground all the way from battery negative on battery , that will help with your troubleshooting . Most likely corrosion problems .

etrailerTeam

Since nothing's working with the trailer plugged in but not hitched, it would seem to indicate that the trailer's been getting its ground connection through the trailer ball.

The most likely place to find the problem is the spot where the ground wire from the trailer connector grounds to the trailer frame, usually on the trailer tongue. Make sure this connection is tight and not corroded.

If you click the provided link, you can see some other troubleshooting strategies as well as some help articles and a ground troubleshooting video.

https://www.etrailer.com/expert-159.html