I have a 2002 F-150 XLT with what appears to be a factor installed trailer harness (4 terminal plug). I'm not getting any lights to work on any trailer, seems there is no electric current from the connector. I can't find any fuse problem and as far as I can tell the wiring harness appears to not have any damage. I need a fresh start to trouble shoot it but am not familiar enough with this type of wiring harness to know where to start. I don't even know where there is a connection for it. Any helps or tips would be greatly appreciated. I have installed plenty of packaged trailer harnesses but this is a bit new to me. Standard wiring colors are no issue. Finding where it is not making electrical contact is the issue.

 

Look at fuse 5 and relay 201 in engine bay fuse box.
The harness connector is up on the driver side frame over the rear wheel area.
Good luck.

 

Thanks much! I'll be checking that out shortly after daylight gets here...

 

Assuming they never worked during the whole time you've owned the truck, look in your glove box and see if the relays and fuses are still in their plastic bag.

 

Something crazy going on. The tail lights are working. I checked at the harness connector near the driver's side tire. Got power there from flashers. No power to terminals on end. When I checked wire colors, voltage and continuity of terminal harness the wires do not correspond to the "Hot wires" on the female end of wiring harness from truck. The colors for brake/turn signals are yellow & green. The color of wires on the truck harness female end appear to be green/red and (my sight is not good) either orange or red and blue or purple.. they're upside down to where they should be. Not sure if there is a problem somewhere else or if I should just cut and tie wires together to make it work or what. I hate to jerry rig things....

 

you realize the tail lights and turn signals are not tied into the trailer light wires ? The trailer has its own wires and fuse separate from the truck lights.

 

Zackly why I'm asking all these stupid questions...

 

Zackly why I'm asking all these stupid questions...

 

I am assuming the wires/female terminals I found that were getting voltage are for the lights on the truck.. stands to reason that the yellow and green are not getting power from the harness either due to a break or no contact at other end of wire loom.

 

About page 205 in your operators manual it should show the fuses. I think #19 and #20 in the box on the left fenderwell are for the trailer running lights. Also check the breaker and fuse that Bluegrass mentioned above... THe truck harness at the spare tire left side should have several wires in it. The rear harness to the tail lights and 4 prong trailer plug will have a couple less wires. The wires missing will be the brakes and battery charge for the optional trailer feed for 6 or 7 prong plugs .... You should be able to trace the 4 prong wires up to the plug by spare tire. Should have voltage on one when running lights are on, and another when brakes are on.. Make sure you have a good ground wire !! If no power, then look up front at the fuses.

 

Again, some of the wires are TRUCK LIGHTS and some are TRAILER LIGHTs... not the same.