Trailer wiring/light problem

If a trailer light fails my first action is to give the connector a squirt of contact cleaner.

The quick and dirty test for bad ground is to take connect a jumper cable from the frame of your truck to the trailer frame and see if the problem goes away.

I have a 2010 f150 XLT. I'll test the trailer brake testand check the grounds.

Thanks

I would lean on bad ground, but there could be other possible causes. But, usually bad ground will make some other lamp light dimly, because the current is back feeding to find a way to find a continuous circuit.

ALL LIGHTS MALFUNCTIONING means an error common to all.

That would be CHASSIS NEGATIVE.

Have a 2nd person man the brake controller when you're doing your testing. If the lights act screwy and then go out altogether when trailer brakes are activated you can take BAD CHASSIS NEGATIVE to the bank.

Negative wire from tow vehicle frame to socket. Many many bad connections to truck frame.

Negative wire within socket and or plug

Negative wire from trailer plug to trailer chassis

Welcome to the forum. Although your description points to a bad ground, you've given us little to work with. What vehicle is this? What has been done to it recently?

Yep. More times than not it is a bad ground.

Moved from Forum Technical Support

Sounds like a bad ground some where on the trailer.

Check your ground?