Ok, so here's the deal: When I tow my boat trailer during the daytime, all the lights work correctly. When I tow at night, it seems as if the brakelights on the trailer are always on, and when I turn on the left turn signal, the arrow just lights up, it doesn't blink. It doesn't blink outside the truck either, and doesn't light up like it does on the truck. If the running lights are off, it will work correctly. Any suggestions? I'm thinking the wiring is messed up somewhere on the trailer...

 

You have the 12V and reverse light relays hooked up? My left turn signal wouldn't work at all when I didn't have those plugged in.

 

Start by removing the 1157 bulbs in the trailer tail lights/markers. This is a double filament bulb so it does both. Now try the lights again. Do they work correctly as far as running lights on the rest of the trailer? If so you probably have a corrosion problem in one of the tail light sockets, or a bulb was installed up side down. Re-install the bulbs and see if it works correctly now.

If it is still working wrong you need to check your wiring.

Start by checking the truck 1st. Next I'd check the trailer wiring connection at the connector. Finally trace for shorts between the brown wire and the yellow and green wires. Make sure you have a good ground on the white wire...this causes all kinds of weird problems.

Good luck.....

 

I'm going to check the trailer wiring first, I noticed that it was redone at the plug, and it doesn't look like it was a good job either

 

Double check the white ground too- I've seen the lights do really weird things when not properly grounded.

 

It's properly grounded, all of the other lights work fine. It's just when the running lights are on, the right turn signal won't work on the truck or the trailer... Actually, I'm not to worried about it, I hardly ever tow at night, and the road home from the river only has two left turns that I need the signal for...