Used my trailer this weekend . I have the trailer tow package. The "12v" at the plug on the truck has no power. Manual says there is a 25 amp fuse under the hood at position 30. It is there and good. Any Ideas? Thanks

 

I found a guy on the F150 forum site that said the truck had to be running.. the left driver door shut ,.... and the keys in the cab for the 12volts to show up on the trailer so it sounds like you can't check it ...

Also they a guy said the negative was at the 7:00 and the positive was at the 1:00 and the description on my plug cap is the opposite.. 2018 Lariat... any Ideas...

 

Isn't there is a thing with the truck needing to "sense" the trailer to provide the power. There's some kind of "smarts" to the system that makes it hard to test, especially by yourself. Can you use one of these and a second person int eh cab of the truck?

 

Some clever person put the pin-outs for the bargman connector (AKA 7-pin connector) right on the dust cover (see below).

It's also true that the trailer needs to be connected and the engine on for the +12V to appear at the connector. I test it by having everything hooked up, and measure the 12V at the trailer battery when the engine is running.

 

The trailer needs to have it's own battery for the relay to power up and sense the load. Did the trailer have a battery?

 

So with this situation, do those testers like I posted work on this generation of truck? Or does the 12V lead remain inactive with them?

 

They don't work on these trucks.

 

Still handy for testing the other pins I guess.

 

Yes the the trailer has it's own battery; a marine style deep cycle. I normally have a small solar charger on it and also a volt meter and a button I press to see the voltage. It was at 12 volts when I brought the trailer home but it didn't have enough power to pull the race car in. I left a regular charger on it for the day and still had a problem. Not as much. I'm going to do a battery test tomorrow. The electric jack is always tough on it too.
I was hoping that the solar would keep it a a higher level.

 

How old is the battery? Water level OK?

 

My 2015 did not have the power wire from the battery to the big plug in the back. It had to be added. Mine had tow package, too.

 

Resurrecting this old thread. We haven't been pulling our TT for a while, and I know this used to work. However, we towed about 5-6 hours the other day, and when we got there, the battery in the TT was depleted. I tested the power at the trailer battery with the motor running, but there was no charge voltage at the trailer battery (it was showing 12V, but not charging). Looking through the fuses & relays and there is nothing that says battery/or 12V for the trailer. Did I burn out the wire or something?

 

if a fuse was installed, as it should have, it is aftermarket, its not in the fuse block. mine is attached to the postive battery terminal.

 

I am in complete amazement at the quality of most trailer wiring... assuming it was done by a 7 year old. I've found connections that were just taped together or connected with wire nuts which work great for the first couple years, but left exposed to the elements eventually corrode themselves to death.

If your TT is anything like mine, the harness from the truck goes to a "splice box" or something similar mounted to the frame of the trailer near the front. From there, wires come out to go to the battery (mine is connected through a resettable fuse) and to other places. Open that box and look for shoddy workmanship and fix anything that looks suspect. Also, find the place where the ground is connected to the trailer frame and fix or clean as necessary.

Oh, and just to be sure (because I've done this before) did you check to make sure the battery disconnect switch is turned on?

-- Gabe

 

This TT does not have a disconnect; at least for that. I will check the TT wiring as it had been sitting for a while.