m1101 light not working when truck door is open

Got my M1101 the other day. Got a cable from Eriks Surplus to convert from the military connector for the lights to my Ford F150. Works great.

Except.

When I open a door on the truck, the left light goes out.

Just the left light. As soon as I shut the door, the left light comes back on.

I swapped bulbs with the right side light, but still did the same thing. I also replaced the lights bulbs with new LED ones, still did the same thing.

And thoughts on what could be wrong?

Let me see if I can post a video of it....
https://drive.google.com/open?id=16teAwweD5lXLmq8ViNEHFSKgjolWaDI0

Please ignore the junky backseat of my truck.

If it was a bad connection or short or something, how could opening the door affect it?

The only thing I can think of is maybe opening the door drops the voltage, but them why does the right light still work?

I would like to figure this out.
Thanks!

-Mike

That is a very puzzling problem, but I would think the problem has to lie in the truck, not the trailer. I couldn't tell from your video, but does the left light on the truck mimic the trailers left light in that it also goes out when the door is open?

That is a good question. Let me check...huh.

The truck lights work no matter what. door open, door closed, all doors open, three open, whatever. Even tried turning on the lights on the camper shell. Still get the left turn signals on the front, rea mirror, and rear of the truck.

But.

Now the left light is not working at all on the trailer!

No matter what. Door open, door closed. I tried whacking the side of the trailer, and jiggling the wires a bit, nothing.

I assume it's either the light fixture or the wiring.

Is there an easy way to tell?

I would start checking grounds .

Trailer left light ground is my first guess.

Erik's connector / plug contact is my second guess.

I also think you should check grounds

Check grounds but also DRIVE WITH DOORS CLOSED.

Video wouldn't play for me. What year Ford? Does it have a relay setup for the trailer lights? If so, check that first. When I was running those aftermarket controllers for trailers on my 09 Ford Escape, they frequently failed in weird ways. After discovering it had a complete factory setup except the relays, bought 3 relays, plugged them in and now no more problems.

I have a suggestion. Drive your truck to the nearest U-haul trailer rental and ask them to let you connect the U-haul trailer wiring on one of their trailers to your truck and see what happens. You can tell them that you intend to rent a trailer later but just want to check out your truck to make sure everything is OK. This will eliminate your truck as a problem if everything works with the U-haul trailer.

glcaines said:

I have a suggestion. Drive your truck to the nearest U-haul trailer rental and ask them to let you connect the U-haul trailer wiring on one of their trailers to your truck and see what happens. You can tell them that you intend to rent a trailer later but just want to check out your truck to make sure everything is OK. This will eliminate your truck as a problem if everything works with the U-haul trailer.

Click to expand...

Depending on what plug is on the truck you can buy a test plug for pretty cheap.

https://www.amazon.com/Trailer-Light-Inline-Circuit-Tester/dp/B003EEV4HW

Slight update.

The truck lights work fine with nothing attached to them. Door open or closed, everything works.

Drove out to my BILs farm and hooked up my 20 ft trailer, and it too works as it should, doors open or not.

So it's not the truck, or the connection on the truck.

I traced the wires and found a ground point. It looked ok, but I took the bolt off and am cleaning it up and cleaning up the spot on the trailer it attaches too.

I thought with all this extra daylight I'd be able to work on it more, but apparently the wife has had a list of stuff I need to be doing while it's light outside instead I may be able to fiddle with the ground this weekend.

I'm curious why you went with a very expensive adapter, when you could have easily and cheaply disconnected the mil harness back at the first junction underneath and wired in a proper connector that would fit your truck.

Are you planning to pull the trailer with a mil vehicle too?