I have a 98 f150 that I can't find what is wrong with the trailer plug. I plugged into my trailer 2 weeks ago and it worked fine. Now the only thing that has power is the positive wire. The running lights work when plugged into the trailer but not the turn and brake lights. When I ohm the other wires to the ground wire (on truck) they are all open. I did the same on my neighbors plug and the turn, brakes, and running were shorted to ground. I plugged my explorer into it and it acts the same way. We are talking the standard 7 wire plugs on all.
The trailer is less than a year old. When I ohm out the wires on it, they are all shorted to each other. I guess they all have a common ground.?
Note all lights work on each vehicle as they should. I have checked all the fuses under the dash and in the power distribution box. Does anyone know if they are more fuses to check somewhere else? The ground IS shorted to the chassis.
Should I not get a voltage at the truck plug for the turn and brake lights?
Anyone know of a place thats shows where the turn and brake lights on the truck's plug gets it's power from or if there is some inline fuse between the fuse boxes and the back of the truck.
I hooked up to a known good trailer and the lights don't work on it either. So my guess is that the trailer has a short in it and it has taken out some fuse on both my f150 and explorer.

thanks for any help!

 

If you have factory plugs on your vehicles, then you have the tow wiring, and it has seperate tow fuses. Look in the fuse box inside, and also look in the fuse box under the hood.

If you have a small battery charger, I would use it for testing the trailer wiring till I found the problem on the trailer. The charger has circuit breaker that will trip before it ruins the charger, or melts the trailer wiring.

 

Yea, I checked both fuse boxes. The charger is a good idea except the trailer is stuck in a storage place. thanks for the reply.

 

Your 1998 F150 has a THIRD fusebox that has the fuse for the trailer/brake circuit.

The mini-fusebox is located near the corner where the driver's side inner fenderwell and the firewall meet.

Look at F2 - 20A. it's probably blown.

Steve

 

Where is the 3rd fuse box, inside the cab or in the engine compartment?

 

It's under the hood. Must be near the hood hinge on the driver's side from his description.

 

Ok - I found it and it was blown. THANKS! Now I have to fix the trailer. I think that the brake controller must have been wired wrong and shorted something out.

 

That's only a 20A? Chevy's have a 30A for that fuse. Most of my customers find the short near the trailer brakes. That's where the wiring is the weakest. Lots of connections and alot of abuse. If not there it might be a dirty 7-way plug.