Not sure which fuse you checked.
The Engine Compartment Fuse Panel ( Battery Junction Box / BJB ) is where the fuse is for the trailer tow adapter parking lamps.
Fuse # 5 is the fuse for the parking lamps, and the reversing lamps.
Next is the trailer tow adapter park lamp relay. This is what BJB Fuse #5 feeds, and the coil is operated by the truck's parking lamps. This is also in the BJB, Relay 201, it is the 1/2 size relay.
Not sure what you took a resistance reading from on the trailer tow adapter.
If you want, you can pull the trailer tow park lamp relay, and jumper the normally open contacts, which should provide power at the trailer tow adapters, regardless of the truck's lights.
This is the wiring diagram for the trailer tow park lamps
1. What kind of vehicle do you have?
2. Have you verified that the trailer lights are working. You can run a wire temp directly from your battery to the trailer running lights usually the brown wire on your trailer.
3. Don't forget you must have a ground to the neg side of power source in testing.
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