I just spent a frustrating weekend with my new boat trailer. (well, new to me) And my 2004 STX

Had issues with this working here, that not working, etc., etc... So my Dad and I pulled all of the wires out and rewired the trailer. Problem is, it still won't work right.

1 Parking lights work fine.
2 RH trailer will blink the correct filament (separate from the parking light)
3 LH Trailer will blink the parking light filament on and off (even if the parking lights are on- it's un-signaling them I guess I'd say for ease of explanation...) for the signal... But not the regular signal filament
4 Brakes will light up corrctly (second filament) on the RH trailer
5 Brakes on the LH trailer kill the light in the bulb entirely. Let off the brake and it comes back on. (That's why I think it's un-signaling...)
6 Flashers do the same as the turn signals.

We have double and quintuple checked everything, tried swapping wires to the opposite poles in the lights, and it behaves no differently.

Plugged them into my Dad's 2004 SCAB and it does the same thing.

I mean- it isn't that hard- green/green brown to one side, yellow, yellow/brown to the other, white grounded. I don't get it... We even tried different trailer lights from a spar trailer, and it does the same thing.

Has anyone had issues with their wiring placement in the trucks? Is there a fuse/relay that could be causing this? It does it with both the flat-4 plug AND the Round plug converted to a flat-4. I hooked one of those little trailer wiring testrs in the truck, and it checked out fine.

AAAAHHHHHHH!!!!

 

I'd say the problem is with the trailer wiring, it appears you have a bad ground somewhere. I have an '05 F150 and my 5 pin boat trailer is plugged into the round outlet with an adapter I bought at Boat US. All lights and brakes worked fine right out of the box.

 

I think if you are using a round type plug you may be wiring the plug on the trailer side wrong. install the connecter in the truck plug. then use a test light to see where the proper wire should go .

 

Is the traler hitched to the truck. or just parked by it?
I have had strange things happen when I've only backed the truck by the trailer and pluged things in. The trailer needs to be on the hitch ball to get a good ground.

TFB (Bill)

 

Sounds like a bad ground to me. As Toolfreak said, make sure that you hook the trailer up to the truck, most of the time that is the problem. If that doesn't solve it, sorry that I couldn't be of more help. Since I am alot better at being hands on, rather than just talking about it.

 

I agree with the others, it is a bad ground. It is backfeeding through another circuit to get to ground. When you put two signals to the light (brake and running lights), it loses the ground and goes out. I'll bet the one that fades is at a lower brightness than the one that works properly.

A volt meter and/or a test light will help. Both are good investments and you should be able to pick up both for well under $30 (assuming you dont already have them).

 

I'll have to hook up the voltmeter tomorrow. The trailer lights function the same whether the trailer is hitched or not. Where could the bad ground be? The white ground wire is ground well and bolted tight to the trailer, and the ball is new- would the light itself be the only other ground? Not sure where to look for the bad ground... (?)

Thanks for all the replies!

 

Sounds like the only thing you have not tried is replacing the trailer plug. You've tried different trucks, used new wire, different tail lights, the trailer is hitched to the truck. I don't think you have anything left but the plug on the trailer side.

Good Luck

TFB (Bill)

 

How old is the trailer? Sometimes the fasteners and/or the light mounting brackets become corroded and fail to ground properly. The lamp sockets may not be grounded, the ground wire or power wire may be broken or damaged.

 

I have had the same issues with my trailer. I mostly have brake light issues. First, when you hit the brakes, only with the parking lights on, the left light would go out completely. Took apart and cleaned the mounting surface for the light( grounds through mounting bolts)- fixed. Next time I went to use it, r/s is doing the same thing. Haven't fixed it yet, but have verified it to be a bad ground. Also if it's like my utility trailer it has the cheesey, likely rusted liscence plate bracket mounts between the light and trailer frame( or nuts and frame)-- make sure that is cleaned up too. Verify that the main ground on the trailer frame is good. Just by reading what it's doing and what mine has done, I'm going to say you have a bad ground somewhere on the trailer. Reading back to it being a boat trailer, Are the lights sealed units? I know that the unsealed ones on my trailer are badly corroded inside from water entry, contacts, bulbs, everything. All I can say is have fun with it and learn it. Because it's a trailer you'll have to fix it again sooner or later. Also, do you have a multimeter available to you? If you do, check resistance from the lights to ground, any more than .5 ohm, find and clean your grounds. If not clean them all up and try again.

-Scott

 

Thanx all, it was a bad ground on the LH rear light. Nothing should be bad now- New plugs, wirs, lights, bulbs, and license plate (since I just bought it!)

Thanx again for all the help...!

JD