Drove the truck to school today because I didn't feel like riding in the rain. Was stopped at a light with the right turn signal on when I noticed that it was flashing without the flasher can clicking. The flash rate was also greater than normal. It also only seemed to be doing it while the brake was applied. A short while later the ABS light came on. Before I've only had problems because the trailer lights were shorting out. I do have a cabover camper hooked up, but have never had problems with its wiring.

 

Issues like this generally point to a bad ground. You said it was raining...check for leaks in the lights. That would be my first step...

 

Have you checked the turn signals, four-way flashers and brake lights?

 

Update: The left signal also flashes with out the flasher can clicking. This is also intermittent, and only when the brake pedal is pressed.

It's been pouring all day, so I haven't checked yet. I'm assuming they are illuminating, because the dash indicator does, and I saw the reflection of the front turn signals driving home. The center mount brake light works; I can see it in my rear view mirror. I'm kind of hoping someone else has experienced this, and knows a solution.

I need to disconnect the camper harness, and hitch extension wiring to see if it's in the truck, or the trailer wiring. But that requires crawling on the ground; which can wait until it's not raining. The truck isn't getting driven again until Sunday anyways, so I'm not in a big hurry.