brake lights notworking

[iviper123]

i work on my boat trailer wire harness fixing it and found out my brake lights dont always come on, sometimes they work fine and others dont work at all, or the flash for a second and turn right off.

Bad stoplight switch?
if yes how hard is it, it look like lots of fun...lol

 

[millsroger]

Do the brake, tail and flashers work on the truck with no trailer connected???

 

[iviper123]

1

Do the brake, tail and flashers work on the truck with no trailer connected???

Everything else's works fine with or without a trailer

 

[3500GMC]

Ground issue?

 

[NVW]

Ground issue?

Grounds are my usual trailer light problem.

 

[millsroger]

If the flashers work on the truck then it is either the brake switch or the flasher switch or even the EM flasher. When the flasher switch is in center it connects the brake circuit and EM flasher to the same lites. Hold the brake and cycle the turn signal and EM flashers to see if one of them is intermittent when centered or off. Have seen both go bad with too many trailer lites with home brew trailer kits.