i've had a flat 4 trailer wiring setup on the truck for a while now (plug in style)
i've just added a brake control box with 7 pins. my backup lights did not work before today, and my hazards haven't worked for a while. here's what is going on.

with the trailer plugged in. blinkers work. running lights work. when the running lights are off, the brake lights (running light strength) come on. if the running lights are on and you hit the brakes the trailer lights go out. also if you connet the positive and negative on the 7pin on the truck the backup lights come on i've also noticed that when the brakes are applied with the trailer plugged in the backup lights come on very dim with it. please help, i have a long trip to make tomorrow and need to get this sorted out.

 

stuff like that was happen when i had a light socket on my camper touching ground the pos. side

 

Start with a good ground. Most trailers are grounded through the ball and that's bad. Run a separate ground to the frame of the trailer, through the 7 pin plug and go straight to the truck battery. After that, things should start getting better, or at least much easier to figure out.

 

do i have to go all the way to the battery? (running out of wires, lol.) what about grounding it good to the frame rail? i can't find where the original ground would have been. i was told there would be a self tapper into the frame.

 

You don't have to go all the way to the battery but it really seems to make a difference. On the newer trucks the 7 pins have one pole wired that way. I had to rewire my trailer plug today and in doing so found the trailer was only grounded through the hitch. I ran a ground from the trailer frame to the battery ground in the plug. I was not having any light or brake issues but my lights are brighter now.