Odd trailer wiring problem...

[Zrider1967]

Hello all. New to the forum, just getting back into fishing.

I just bought a 1971 Appleby Laker Supreme, which I love so far.

The guy I bought it from put new lights on the trailer, but something is wrong. I'm usually pretty good at wiring, but this has me baffled.

The left tail light and both side markers work as intended. The issue is with the right tail light.

The wrong filament lights up - whenever either the breaks, hazards or right turn is used, it is the dim filament that lights. I've checked the bulb, and it is installed correctly. I've tried a different bulb, and the same thing happens. It seems to be wired correctly - when tested, the green wire flashes, all the way back to the tail light. But wait... there's more!

Turning on the headlights causes the filament to stop blinking all together, and now neither filament is on. But now both the green and brown wire now have a steady current when tested.

Through all this, the left tail light and both side markers continue to work normally. I've checked for shorts, and cannot find anything. If somehow the green and brown wires were making a connection, both filaments should light when anything is on, and the right side marker should flash when the turn signal is on.

Anyone smarter than me have any ideas? BTW, everything works fine at the harness at the truck when not connected to the trailer.

 

[earl60446]

Green is for the brakes, turn signal and flasher. Brown is for the right running lights. Verify that you have 12v from brown to grd with lights on. Nothing when lights off. Verify you have flashing 12v when hazards on from green to grd. Nothing when off. These are readings with bulb out. Always verify you have a good grd, most trailer wiring problems are the grd and/or corrosion.
Tim

 

[Zrider1967]

I know what the colors are for, and like I said above I've tested all wires, and the green flashes when it should if the headlights are off, but the wrong filament in the bulb lights. With the headlights on, the green is steady but NO filament is lit. The green should only be steady if the breaks are applied. So I know what is happening, I just don't know why.

For some reason turning on the lights causes the green to burn steady when it should flash, but the same filament that flashed when the green wire flashed (which is the dull one, not the bright one like it should be), is now dark when the green wire is steady.

I still think somehow the current from the brown is getting into the green, but then both filaments in the bulb should be lit.

 

[lckstckn2smknbrls]

Sound like one of the 2 filament bulbs has burned out one filament and it has fallen against the good filament.

 

[Zrider1967]

It's not the bulb. I swapped the bulbs and the right tail light still had the same problems, and the left one still worked fine.

 

[lckstckn2smknbrls]

Have you tried plugging it into a different car or truck?

 

[Zrider1967]

No, but everything at the truck's wiring harness tests fine.

 

[JMichael]

Go around and clean and double check all your grounds. It sounds like a bad ground doing really strange things like that.

 

[SumDumGuy]

Perhaps the wiring within the light housing is wrong?

 

[dejamat]

I would put my money on a bad ground. try running a separate ground to the light to see if it straightens out. I have seen this to many times in the past. Good Luck! Dave

 

[KMixson]

Sounds like a bad ground. I have seen very strange occurrences happen with bad grounds. It will baffle your mind. You will wonder how in the world can it do what it is doing. You will pull your hair out before finally finding the bad ground.

 

[dieselfixer]

It sounds like a definite right side ground problem they can be a real pita like others have said

 

[richg99]

As many have already said...GROUND(S)...is/are your problem(s).

The new LED set I recently installed came with pre-wired white wires. They were the full length on each side for connecting to the front. No more flukey, inexplicable, strange occurrences such as yours.

Run two new, full length, white grounds and you will never have it any other way again.
Regards, richg99

 

[Zrider1967]

Thanks guys... I'll check the tail light's connection to the trailer. Now that I think about it, that is likely the problem. The previous owner had just repainted the entire trailer, down to every nut and bolt. He even painted the trailer tongue pin. So i'll bet the tail light isn't making proper metal-to-metal contact with the trailer.

 

[richg99]

Just one last thought... One time, I was checking EVERYTHING... and still had troubles. I had failed to actually drop the trailer onto the ball. I just backed the van up and connected the wires. Well, connecting the hitch and ball made everything work. Didn't make a lot of sense, but it fixed the issue. richg99

 

[KMixson]

One other thing, just because the ground wire is bolted to the frame doesn't mean that it is grounded. You have to make sure there is good metal to metal contact on the connectors to be sure. Metal to paint will not work.

 

[earl60446]

richg99 » Today, 08:49[/url]"]Just one last thought... One time, I was checking EVERYTHING... and still had troubles. I had failed to actually drop the trailer onto the ball. I just backed the van up and connected the wires. Well, connecting the hitch and ball made everything work. Didn't make a lot of sense, but it fixed the issue. richg99

Makes perfect sense, some less than desirable wiring configs for trailers rely on the hitch ball to establish the grd. It's a poor way to get a grd at best but very common, especially years ago. If your trailer is only 3 leads, you likely use a hitch ball grd.
Tim