Boat trailer lights partially working

[Jimwhall]

So… I hate trailer wiring. I’m terrible at it. But I have a jam:

The “traffic lights” on my trailer (break, turn signal) work fine. The running lights don’t work at all.

It is a 2016 four winns trailer with a new five flat adapter to my round seven pin Outlet on my jeep commander

Other trailers seem to work fine for the commander.

I have done cursory checks of the plug in the wires and they seem fine. How do I even begin to troubleshoot this?

 

[ThomW]

I would take a battery and jumper cables. Connect the jumper cable ground to the battery and a good ground on the trailer. Then connect the jumper's positive to the battery and with the other end touch each of the 4 prongs on the flat 5 adapter, one at a time. While doing it, have someone verify if the lights work as they should. If you put power to the one for the running lights (brown wire on mine) and the lights work, its an issue with the adapter or jeep's plug in.

 

[dingbat]

My first step in troubleshooting would be to replace the 5 pin with a 7 pin connector.
Adapters sux. Nothing but problems in the long run

If the trailer is new to you, trailer wiring is not "standard" by any means. I've had to rewire half of the trailers I've owned to match the truck.

Once you know the wiring matches, check the ground between the truck and trailer by taking an ohm reading between the ground pin in the connector (trailer side) and the ground connection on the trailer.

Ideally should read 0.0 but anything under 2.0 ohms will suffice. From there check for continuity between the ground and brown wire(s) on the trailer. If you don't have continuity, you have a burnt bulb, broken wire or a dirty connection somewhere.