I recently converted a 7 pin round connector to a 7 pin blade (RV) style. Everything worked at first. I used a test light and my wife working the lights, brakes and brake controller to confirm the function of the wires. Later I was confirming the 12v slot to connect to an electric trailer jack and accidentally touched the trailer ground to the 12v (fat fingers and darkness) As expected the 12v wire sparked and went dead.

I figured I popped a fuse. The tested every fuse with a test light and visually and all are working. I swapped the relays using a known good relay and everything test fine at the power distribution box and fuse box. The 12v line at the plug is still dead and all the other wires don't register power (tested with the same test light as when I first converted the plug). The test light is working. There is a separate 4 way flat plug that was previously wired in and it is dead too.

Now here is the weird thing. If I connect the trailer, then the plug works...brake lights, tails, turn and trailer brakes. Even the 4 way flat plug goes live and works as designed. At least I can move the trailer around, but I want to fix it the right way.

I am guessing that I have a ground problem somewhere between the plug and chassis. I am not sure how touching the trailer ground to the 12v truck plug slot messed up the truck ground. Worse I can't find a break in the truck plug ground.

Anyone have any suggestions?

 

If you want to verify you really do have a ground problem, move your alligator clip on your testlight from the plug ground to a clean spot on the frame or bumper and see if you do start getting light signals. You could also test your 12v power terminal and see if it comes alive again.

If you find you do have a ground problem, and you can't find the problem, just run a new ground wire from the plug to the frame somewhere.

 

Here is the latest. I unscrewed and then reattached all the connections at the 7 plug at the truck. This was what I had converted from 7 round to 7 blade RV so I figured one might have come lose.

I now get a good test if I use the plug ground to the 12v. However, if I try a ground on the frame or other body part then the test light does not light up which I find odd. If I use the bolt where the ground for the plug is attached to the frame, then all is good, but not on any other part of the frame. Odd right?

The good news is that connecting to the trailer powers all the lights and brakes as it should. I would just like know what is up with the 12v not testing unless I am using the ground on the plug.

 

All I can say is rust.