Running lights and marker lights on trailer stopped working. Brake and turn signals work. Which fuse # or relay # needs to be replaced.

Check the bulbs and grounds at the trailers marker lights.

Troubleshooting No Running Lights on Trailer but Turn Signals and Brake...
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Thread Running lights on trailer don work but turn signals and brakes do

Check some relays, most of those lights are driven by relays and a fuse.
Hope this helps.

Try the specified fuses in the under hood fuse center. they are common to blow.

CHECK THE FUSES IN THE BATTERY JUNCTION BOX # F34 25 AMP CARTRIDGE TYPE FUSE FOR TRAILER STOP/TURN RELAY
ALSO CHECK #33 IN THE SMARTJUNCTION BOX IF THE BRAKE CONTROLLER ISN'T WORKING

HOPE THIS HELPS

It is a possible option that the relays for the Stop / Turn are having an issue or the fuse in the Engine Mini panel is blown ( page 142 of the 1997 owners manual )

On the 1997/98 MY this is in the aux relay box in between the Engine Compartment fuse panel and the engine mini fuse panel.


The output of the MFS ( Multifunction switch ) triggers the relays, to use the trailer tow fuse to operate the trailer lamps. The fuse to supply power to the Normally Open contacts on the trailer relays should be hot at all times. You can verify this with the diagram below by metering from pin #3 to pin # 2 [ground for coil] or to another known ground.

These are 1/2 size Ford ISO relays, and can be jumpered to make testing easier ( and with this diagram you can bench test them with a meter to check resistance over the Normally Open contacts, when applying power and ground to the coil ).


I am not 100% sure on the 97/98 MY F-150 about the location of this connector, but the 99-03 have all the wires to the rear of the truck via a connector along the driver's side frame rail, that you can check for ( easiest with the spare lowered )


Start with the Fuse in the Engine Mini panel, to see if the 20A fuse is good and work back towards the trailer tow adapter via the relays. I am going with the obvious blown fuse for the Stop/Turn lamps for the trailer.

You should have a separate trailer running light fuse in the under hood fuse box (check you manual).

If you have trailer lights make sure you don't have a short in the connector or harness. You obviously have a short somewhere after the fuse. Try unlpugging each running light. to see if its in the light connecter. also check the side markers

The truck is protecting itself from the load impose by the trailer.. Chk the plug on the truck for wire gauge size. Turn any electrical loads off on the trailer, any and all. If fuse still blows then the fuse is either underated or the trailer has a dead short. In fact turn trail main power panel of. All lights work you say. So ck the inverter for defect byturning off the inverter on one of the trailers.

It should have a fuse for the marker lights. Do they work on the truck. Brown is the color for the marker lights. Good Luck

You can purcahse a tester which will connect into the F-150's wiring harnes. If the led lights up, the problem is witht he trailer's wiring harness. this tester will indicate the proper operation of the brake light and turn signals.