Originally Posted by Uncle Bubba

Doin some lookin through parts books here and it looks like the factory harness for your truck plugs right in under the rear end, should be nothin comin from the front of the truck to control just the trailer. A replacement factory harness is only about 3 feet long. It's all fed from the truck wiring to the rear. So if you have no power to the back of the truck you have a problem in the truck lights. In the end this tells me that you probably have a grounding problem and just need to clean all the grounds off and smear some di-electric grease on them. I also keep the terminals filled up with this grease to keep them from corroding myself. Wish I could offer more help here.

Originally Posted by motodad

I did start at the plugs.
There is power to the plugs, both circular and straight plugs have power going to the running lights, neither have power going to the signal lights. I have power to the running lights, just no signals or brake lights.

Originally Posted by Benjamin

dumb question again but did you test the plugs with the brake pedal pressed? if the brake pedal isn't pressed then there will be no power to the plug. if there is no power there after the pedal is pressed then i'd look into the brake switch under the dash that turns the brake lights on. have you changed the fuse that you replaced with another good one? i've seen some fuses look good and be bad before.

just thinking outside of the box here and my post is not to make anyone feel stupid cause i've made mistakes too when checking stuff...... just going back to the basics....