This is weird. I just bought a new small trailer to haul around my motorcycle and tow by my 97 F150. Now I finally got all the lights on the trailer to work, had to replace a fuse, and the turn signals, the tailights, and the side markers work just fine. Now here's the weird part - the left side trailer brake light stays on all the time as long as the trailer electrical is connected to the truck electrical. It remains lit even if the truck is off, the brakes are off, and all other lights are off! Now I've checked all fuses, checked the ground at both the truck side and the trailer side, and appear that they are good.

Why the heck would just the left side brake light stay on all the time like this? The right works fine,as do all other light functions on both sides.

It's a pain because very time I stop somewhere, I have to disconnect the electrical to the trailer so the left side brake light does not stay on and drain my battery.

Any ideas?? Thanks.

 

Your left trailer light is on, but your left truck tail light is off????

Fricken weird?

You/previous owner didnt happen to splice into a 7-way harness to get a 4-way flat plug did you?

I know one of those 7-ways have a hot wire all the time? But thats about the only thing I can think of?

 

Sounds like you powered up the left turn siganl circuit from the electric brake battery supply.
The wiring is incorrect.
Start by listing what connector you are using. 4 pin, 6 pin or 7 pin.
The next is to ID the working voltages at the connector such as the left and right turn signal operation then hook them up to there respective sides.
Next is to ID the parking lite power and hook it up to the corrrect trailer lead.
The ground lead passes thru the connector to the trailer.
It's not hard to figure this out to what you need to have.
If the trailer is very light weight and needs no trailer brake control, then you would not use the trailer emergency brake voltage supply.