Help with Trailer Lights???

[cory0789]

I am having trouble getting the trailer lights to work on my boat trailer, whenever the running lights are and I hit the brakes the left light completely goes out on the left side but on the right nothing is wrong... can anyone tell me what is going on here is it my trailer wiring or is it the wiring on the truck???

[Selectron]

It would be difficult to diagnose without looking at a wiring diagram, but have you replaced a light bulb recently? Lighting problems which only exist when the brake pedal is pressed are often caused by having inadvertently fitted an 1156 bulb (single filament) instead of an 1157 bulb (dual filament). If you aren't aware of the difference, it's explained quite well on this page.

If that isn't causing it, then could you provide more details - truck make and model, and also a more precise list of symptoms - i.e. do the truck's lights, including brake lights, all work normally with the trailer connector unplugged? And then when the trailer is plugged in, you say "the left light goes out completely", but is that on the truck or the trailer, or both? When you say it goes out completely, I assume you mean both the tail light and the brake light, but does the tail light remain lit on the right-hand side and does the brake light work on that side, on both truck and trailer?

[MagicRat]

In addition to the above, the left side light may have a bad ground. I would suggest rey a new 1157 bulb and clean up the housing ground wire or mount, if it relies on a chassis ground.
Also, check the ground wire for the entire trailer. Do not rely on the trailer chassis grounding through the hitch. If problems still persist, try a new light housing on the left side.
Boat trailers are notorious for rusting out the light housings, electrical contacts and sockets because they regularly get immersed in water.

[curtis73]

Whenever you get funky unexplainable things like that, 99.9% of the time its a bad ground.

[khooper]

1) I've learned more than anything to unhook the lights before backing the trailer into the water. Nothing like a hot bulb meeting cold water.....but if you believe the advertisements, boat trailer lights should be waterproof and not let water into the space where the bulb is. RIGHT !!!!
2) Now, the other issue that has to do adequate grounding usually needing more just the hitch ball. - inadequate grounding is the number one cause of trailer light problems and cause all kinds of strange behavior (work sometimes, or only when headlights are off, or both sides flash with either blinker, etc.) - try a better ground than the tongue and checking for any corrosion at any of the individual light ground connections (which tend to corrode over time).
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Exedy Flywheel