99 ford truck running lights, brake and turn signal work fine, factory trailer wiring, my trailer running lights will not work, brake and signal are fine. Everthing works on my other truck.I have used a meter and have no power to the running lights at the plug. I can find no fuse blown.

 

are you aware of the fuse in the engine compartment?
all the trailer lights are fused in the power distribution box under the hood

fuse 5 - running lights
fuse 19 - right stop/turn
fuse 20 - left stop/turn

 

If you don't have you owners manual, a quick search here will show the locations to download the PDf from ford.
or
There is a sticky at the top of the towing forum that lists them
https://www.f150online.com/forums/to...locations.html

 

I had a problem with mine the other day but the running lights worked and nothing else. I had to clean the t harness plug with all the rain in WA. it was coroded inside the plug. Good luck i hate chasing electrical problems. to many wires.

 

Both my 99' and my 01' did this. In both cases the factory wiring up under the rear end (above the reciever) broke or rubbed something and made it fail. Take a test light and find the hot wire for parking lights in the harness, you might have to follow the harness on back in under the truck a good ways because you dont know where it broke at. When you finally find where the wire is still "hot", simply splice it in and re-route it back to the connector. Thats the right way. However it was easier to me to just pull the back left taillight, splice into the wire for the running lights and run it back down to the connector. If you travel on rough roads (like me on the farm) it seems to be what caused it to break. This may not be your problem but hope it helps.

 

The 99 factory manual that came with this truck has the trailer running lights on fuse #1 with the information you can not find the problem. The fuse #5 is the problem, the manual has the wrong info. Thanks for the help.