I just went through the whole 4 pin to 7 pin conversion along with the relays etc. Everything went fine; so it seemed. When we went to pick up our tent trailer, almost nothing worked. It turned out that the right signal, and tail lamps did not work. The cause was blown fuses. And I had never towed before. The only thing that I can think of is that they blew when I removed the old 4 pin or when I plugged in the new 7 pin. The manual says to disconect the battery when putting in the relays. That seems to be what I should have done when changing to the 7 pin wiring harness as well. We replaced the fuses and everything has been working fine.

 

I just made the same mistake last weekend putting in my KC Daylighters. Ended up blowing the in-line fuse on the line from the switch to the relays. Had everything else done and had to run to Autozone to get a 3 amp fuse. Dang it. But the lights are working now.

Hunt

 

I have the same problem! I made the conversion, but I have not voltage at the trailer brake wire. My stop, turn, and marker lights work, just not the trailer brakes. My fuses do not appear to be blow, but perhaps they are and I just can't see it? I am totally confused by this "simple" conversion!!!!

 

You will have to add a "relay" for the trailer brake. Yes the fuse is already there but the relay is not. I switched from a 4 - 7 about a month ago because I bought a pop-up trailer.

You should be able to get it from Ford for like $5 - $10 or so. When I switched mine from 4 - 7 pin I never took the battery off and did not blow any fuses, guess just lucky...

 

The only relay I needed for my pop-up trailer was a relay to charge the battery on the trailer. As far as I know, the brake lights should work without adding a relay.

 

I think you misunderstood me. You are correct the trailer brake "lights" do no require a relay, however to have power to the trailer "electric" brakes does require a relay.

 

that's exactly right!!