Trailer Wiring - Right & Left flashing together | Ford Explorer - Ford Ranger Forums - Serious Explorations

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Trailer Wiring - Right & Left flashing together

Hello all, I have an annoying problem, but first, a bit of back story;

Purchased my 1991 Explorer and an old military trailer (1960's M101A1) together. The two were both wired with a 6-pin round connector. I'm not sure why since neither the 12v aux or the brake controller were wired to anything. Anyway, being that I have a Chevy Suburban that's a bit beefier, I mainly tow with it. So I wired up a 6-pin female connector on the Burb, soldered all the connections into the factory splice (I hate connectors and adapters). Everything works great.

A couple months back, I decided to go through the wiring on the Explorer just to clean things up and get rid of splices and junk that invite corrosion. Tested all the wires beforehand, all were color-coded properly, hooked them all up properly with the female connector. I go to plug in the trailer and hit a turn signal... both lights flash on the trailer but not on the vehicle. Same thing for both turn signals.

Since then, I've double-checked my wiring, hooked up test lights and voltage meters to the female connection on the Explorer and everything looks like it should, the turn signals are isolated, good voltage, no ground issues.

Trailer also works great on the Suburban, lights are isolated.

So where did I go wrong? I have yet to thoroughly go through the trailer wiring since it looks pretty hacked up but it works on the Suburban and it worked for the previous owner. The only thing different with the trailer is that I have LED bulbs in the sockets.

The only clue I can think of is that when I turn on the left turn signal in the Explorer, the left light is at full brightness but the right is a bit dim but still flashes with the left.


Blue Bomb!
Elite Explorer
November 3, 2013
Reaction score
North Idaho
Year, Model & Trim Level
1991 & 1994 Explorers
I've got it fixed, swapping out the LEDs to regular bulbs fixes the issue. I'm still really curious as to why it was a problem on the Explorer and not the Suburban.

Also, having both the marker lights and a turn signal on makes the opposite light dim slightly. If you stare at it long enough, it almost looks like both are blinking. They're not so I'm ok with it but with that obvious of voltage drop and knowing that there's tons of splices underneath, I'm definitely going to be rewiring the trailer.