Last time I went fishing the running lights on my boat trailer stopped working but my blinkers, hazards, and brake lights all work. Just not running lights and markers. I replaced the plug in on my truck, new bulbs, cleaned all connections and grounds and I checked relay I had a spare at my house but still nothing.. does anyone have any advice what else is to check?

 

Wiring on the trailer. Probably a loose or cut wire.

 

Also tried another vehicle same results, and put on new wires and a plug on the front no changes.

 

They make a 7 pin plug tester to check the truck wiring, so I would start with that.
My connector at the back of the truck (drivers side along frame by spare tire) had the tab break off. So all my lights worked except my running lights were working. Just zip tied the connector back together.

 

But 2 diffrent vehicles with that? And mine is the 4 pin flat plug

 

Probably the brown wire (tail/marker) is broken at or past the trailer 4 pin connector since everything else functions. Try applying 12v to the brown wire past the 4 pin connector. Also, there is probably a splice somewhere as the brown wire has to feed both left & right sides. Also check the splice.


Listed below are the standard color codes for a 4 pin hookup:
Right turn=green
Left turn=yellow
Ground=white
Tail/marker=brown


The brown wire should be next to the ground (covered pin) on the trailer end. Hope this helps.


I buy & sell a lot of trailers which result in towing and bought a combination 4 pin/7 pin tester on Amazon for less than $10.00. It saves a lot of time fault isolating tow vehicle/trailer problems. Here is the tester part: IIT 7 Blade & 4 Pin Tester Just copy the part number and go to Amazon & plug it into the search block.

 

I will have to give that a shot the boat and the truck g
Have brand new plug ins

 

Now im getting pissed off.. all new connections on every Light and same results

 

There is two little 10 amp fuses in the fuse box under the hood. Two small ones closest to the front bumper. My truck had similar issues but ended up being a blown fuse. Good luck