rewired my trailer with new LED lights. Then spent the remained of the day trouble shooting the trailer lights. After chasing my tail for several hours i began to suspect the truck. Used a volt meter to check the 4 pin on the truck and got nothing. I bought a converter from the round trailer hook up (7 pin?) To 4 pin with the red test lights on it and nothing.. hopefully a fuse. Anyone have some fuse numbers. Under the hood and or in the cab. The old lights were not working. I just assumed it was the trailer. Thanks in advance.

 

Not off hand, however the owners manual will have the fuse numbers and locations.


Your truck maybe missing the fuses.

 

I don't see anything labeled trailer lights. And I don't see any information for the fuse box under the hood in the Manuel

 

I am going to look on the ford fleet website and see if I can figure it out.

 

I looked again in the book and their is a diagram of the under hood fuse box. Not sure how I overlooked it. I see #6 labeled Trailer Tow (TT) park lamp relay. Not sure how to check a relay but it's the only thing I see labeled anything about trailer and lamp.

 

That is what I was thinking. Now check and see if it is even there.

 

Yes it's there.

 

you could try and switch it with one like it.


There should also be another fuse I believe in the cab, where there are fuses as well.


Probably the kick panel.

 

check #9 and 21.

 

I installed 9 and 21 today. They were still in a baggie in glove box. Didn't correct the issue. The lights have worked before without 9 and 21 but I thought I'd give that a shot, no luck. I don't see anything labeled towing or trailer in the kick box in the cab. About to go check the harness behind the rear bumper to make sure nothing is unplugged.

 

Pulled the relay from 9 and swapped it with 6 under the hood. No luck. Checked connections behind rear bumper near spare. They seemed good. The black hose conduit on the back side of plugs on truck is torn. I must have dragged it on something. The wires inside look undamaged. I'm starting to reach now. I hate to bring this thing in to dealership and they just tell me it's something simple.

 

Was thinking about this.


I am wondering if you have to have a trailer brake controller installed to get power to the 4 pin? Having the relays in place is one thing but the missing item is the controller to plug into the pigtail.


I also wonder if it has to be enabled in the computer to work too.


Short of checking for power at various points in the wiring leading back to the plugs I don't know what else to check.


do you have the information screen? Can you go through that and see anything that you can enable?

 

Yes I have info screen, didn't see anything. The lights worked before so I don't think it's something I need to install. I verified my 7 pin tester works this morning before work, I plugged it into a buddies truck abd the little red lights worked. Tried mine again and nothing. It either has to be A) a fuse or relay, or B) something in the harness is broken or unplugged. It's not a bad connection because neither of them (7 or 4 pin) is working. I'm going to take a closer look at the harness this evening if I have time.

 

And you pulled the plugs apart at the rear and checked all those connections-correct?


If that is the case then I would work my way back towards the engine and test at various points.

 

Plan on checking the connections on the plugs this evening or tomorrow evening after work.