Hello,

I just built a "Do It Yourself" trailer. I wired it exactly as it was shown in the wiring diagram, but I have a problem...

The running/marker lights, turn signals, and even the tail lights all work when plugged in and towing, but when I step on the brakes, all the lights go out...Let go of the brakes and everything works again. Is this suppose to happen?

I own a 2002 F-150 XLT Sport, with a 4 Pin(Trailer uses) and 7-Pin towing package, and I am new at towing. I'm hoping somebody maybe has had this problem and can give me some advice.

 

I have had this problem with my boats, now if your using trailer brakes it can make a difference. Since your using the 4 pin, my guess is your not running trailer brakes, my problem was that on my 5 flat to 7 round that went to the truck, I had to switch wires around because it didnt recognize i was in reverse, and I couldnt back up. Now with this my guess would be to experiment with the wires. and look in the truck manual and see which wire is what on the 4 pin. I know on the 7 pin it says it on the cover. Just play with them a little and I'm sure you will get it, I go through it once a year because every boat trailer I have seems to be a little different depending on the trailers year.

 

I know this is revisiting an old dead thread, but, it looks like it has not been answered. At least, I don't understand anything that the second guy said!!

Anyway, I have this same problem. Everything works except for my brake lights. Running lights work, blinkers work, etc. But when the brake is pressed the lights go out instead of on.

History:
1. I had the wiring short out on my boat trailer, so I replaced the wiring and got it working again. My trailer is connected to an '06 Ford F-150 with the 4 pin connector.

2. The bad wiring on my trailer also had shorted out Fuse #10 and Fuse #36 on my truck. I replaced these. I also checked #42 and any other fuse mentioned as trailer related in the owners manual.

Anyway, the trailer is working (4-pin), lights work, blinkers and running, but just no brake lights.

Any ideas? I was thihking one of the relays, but I don't even know how to check these?