Trailer wiring troubleshoot

wiriing,problems,troubleshooting,LWL trailers
troubleshooting wiring

All lights work now except for the right rear park/brake/signal light. There’s about 10 leds, 4 in the middle are the park lights and the remaining are for signal/brake. Rear housing shows wiring diagram (smart). However, the 4 center ones only light up very weak, and with brake/signal applied they do stay one/blink but very weak. So I took off the light and unharnessed the wire (red) for the brake/signal. The feed wire (green) is reading full voltage. I then put the two wires together directly, still not working right.

So I’m thinking it might be the led signal itself. Would it be common for one of those to go?

wiriing,problems,troubleshooting,LWL trailers
troubleshooting wiring

Followup #1

I traced that green wire to under the trailer and discovered a spot where insulation was rubbed out (mid section of trailer). It was bound tight with a zip tie, so a bit surprised to see the rubbed area.

trailer wiring,troubleshooting,LWL trailers
one trouble spot

So I spliced that out and put in a piece to bridge the gap.

Still no luck. From this point the green wire runs right to the plug in the bumper, green wire on the right.

trailer plug
trailer plug

That 5 wire (4 pin) plug plugs into the Reese Towpower plug adapter. So far as I can figure:

  • The white wire is ground.
  • The black and yellow/black wires are park lights.
  • The Yellow is left signal/stop.
  • The green is right signal/stop.

The female ends on the Reese adapter reads good voltage. So up to that point there’s power going to the wires.

The only thing I have not done yet is do a resistence reading from that green male pin to the green wire at the taillight.

So far as I know at this point the green wire runs from the plug to the rear right light and controls the right brake/signal function. I’m thinking the best thing to do is simply replace the entire length of green wire.

Followup #2

Last night I took a spare plug, the plug (see below) and inserted it into the Reese adapter. I then ran a wire directly to the right rear light. The resistence check was ok. With the signal on, the signal flashed but only the middle four LEDs and very weak. I sort of suspected a fault because all I was doing was running power to the light, with no ground or other wires hooked up. At least it flashed.

4 pin trailer wire plug spare
4 pin trailer wire plug spare

Next thing I tried was cut the trailer’s green wire and alligator clipped a 25′ length of wire from the green wire leading from that male plug (below) all the way to the red wire on the right rear light. Then plugged it into the Reese adapter. Turned on the right signal. Nothing. Scratching my head at this point.

trailer wiring troubleshoot
cutting the original wire

Well this is what I get for F’n around with something to save money, then turn around and do this. Don’t ask how I did it. Its done. And now its going to cost me $3,000 or so to fix it. Unless of course I get the idea to try and fix it myself and end up burning down the garage or something stupid like that.

20141013-trucktrailerdamage-1 20141013-trucktrailerdamage-2 20141013-trucktrailerdamage-3

But if you’re curious as to what happened, I had to move the truck to make way for family arriving for Thanksgiving. I went to the back of the truck, seen the wire unplugged, figured “Good to go.” I pulled up the driveway and put it into reverse to park on the other side of the garage. I didn’t stop until I bought up solid…the trailer was still hitched and I didn’t see/feel it as I moved. :(:(:(


A Newfoundland born Canadian with a life long interest in woodworking, baking and anything else that peaks my curiosity.


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