Trailer light issues

[MUhunters]

We have almost completed our trailer but are now having issues with the turn signals. My friend and his dad laid the wiring, and his dad has done this before. Now the turn signals do not work. The brake lights are fine. Originally it was left turn only and they spent 6 hours trying unsuccessfully to find the issue. Now both right and left to not work.

Any suggestions?

MU Hunters

[High Desert]

it should be pretty straight forward. Start by checking for power to each side at the female plug on the tow vehicle, then work towards the back of the trailer from there checking at each connection, including directly behind the trailer plug. Also check ALL the grounds connections, they are the most common problem on trailers from my experience. You will find the fault somewhere along the way. If you're not blowing fuses then there is a break somewhere in the circuit. Wiring probs can be a nuisance, but being methodical in the testing has always worked for me.

[Dale M.]

Most likely grounds.... Most fixtures expect to be mounted on metal, grounded surfaces.... Test fixtures for grounds.... Consider running a ground wire to each fixture from known good ground source if you have not already done so....

Dale

[Tumbleweed_Tex]

Um...does the tow vehicle have individual (yellow) turn and brake bulbs?

[tkteardrop]

Did you use leds? If so, some cars/trucks can't operate the
flashers but everything else will work fine. 1991 4runner as an example.
Otherwise its most likely a ground problem.

[Miriam C.]

http://tnttt.com/viewtopic.php?t=16567

This is a pretty good starting place... And you might have to run a separate ground to get them to work... Ground to the frame of the trailer as an extra.

[DIY-Stu]

Umm. There's a little more information needed.

What vehicle.
Are the turn signals amber on the towing vehicle.
Where are they working when trying to get the lights to work.

Using a simple 12v battery you can test your trailer's wiring by hooking the ground to the only hidden pin then touching any of the three exposed pins with the positive of the battery.

For example: the 1/2 Ton Chevy Pickup does have Red Stop lights with Amber Turn signals. BUT it you look under the back of the truck you will usually see a small pigtail tied up. This tail will have White, Brown, Yellow, Green, Blue, Red or Orange. wires in it.
This is the trailer harness. It's prewired for a 7way trailer plug. Which means Don't touch the existing harness.

So what vehicle do you have?

[DIY-Stu]

As for grounding.

Turn on tail lights, Step on brake. Any lights turn OFF? If yes Ground Problem.

[MUhunters]

Thanks for all the advice, but just remembered an important fact:

We bought the 12 volt magnetic trailer light from HF to bring the trailer home. We used the same wiring to hook up the lights we bought from a camper dealer. The lights are stop and turn combo lights.

[Dale M.]

Thanks for all the advice, but just remembered an important fact:

We bought the 12 volt magnetic trailer light from HF to bring the trailer home. We used the same wiring to hook up the lights we bought from a camper dealer. The lights are stop and turn combo lights.

IF magnetic lights work fine (test) with TV.... Definitely a trailer wiring problem....

And even with all the frustration of problem solving the wiring is really simple....



Dale

[Miriam C.]

A picture of the light fixture and the wiring going to it will help. Also you can run a separate ground to the tow vehicle using a battery clip. Get it at the auto parts store..

Also look in the light it's self and be sure all wires are connected...You would be surprised how often they aren't.

[Shadow Catcher]

A VOM or test light is your friend

Start at the light(s) that is not working and work your way forward, though you might want to check the TV plug first then you know the problem is isolated to the trailer.

[bobhenry]

Topic is TRAILER light issues.

If we take the tow vehicle out of the conversation it will be
very simple to test the trailer.

Get a test battery or just jumper cable to a convenient
car battery.

Ground the negative to the trailer ground. It could be
frame or it could be hard wired all the way back so don't
just assume the frame is ground.

[On my TD there is no negative contact to the frame]

To make individual contact to the different circuits I use
a #1 phillips screwdriver and clamp the hot side jumper
cable or wire to the metal shank. Touch each of the
circuits and have someone observe. If all light as needed,
You have now eliminated the trailer.

You now have a ground issue or a tow vehicle wiring issue.

To eliminate the ground issue hook up as if to tow and
clamp one side of the jumpers to the trailer ground and
the other to the tow vehicle frame.

Still no lights you no longer have a trailer wiring
problem or a ground issue, it is the tow vehicle.

With individual turn and brake light set up you will
have a converter on board. These things are very
fragile. Miswired crosswired or just overloaded they
can easily be fried and are then junk. I am betting
this is your issue.

Keep us posted and let us know what you find.

P.S. If you feel you are over your head a company
U-haul center can get you going in about 10 minutes.
We did thousands of them during the time I was
a center manager.

[Tumbleweed_Tex]

...the turn signals do not work. The brake lights are fine.

If taken literally, this condition rules out every possible problem on the trailer as to why the turn signals won't work.

If the large element in a bulb works properly, or "fine", when the brake pedal is depressed, and does not work when the turn signal is applied, the problem has to be located on the TOW VEHICLE SIDE of the tongue connector. Correctly functioning brake lights prove the trailer wiring, grounds, sockets, and bulbs are all OK.

I too suspect the converter.

[Larwyn]

If you still have the mag mount lights, checking the tow vehicle is as easy as plugging them in to the connector, if the mag mount lights still work, the tow vehicle wiring is fine. The ground for the mag mount lights is hardwired to each socket so they do not depend on the trailer frame to complete the circuit. They make an excellent tester for the vehicle wiring and I have used mine for that purpose on a couple of occasions.

Bad grounds can give you some very strange symptoms sometimes. It is kind of hard to describe but when the dual element stop/turn/tail light sockets are not grounded you end up with an alternate path to ground through the non energized filaments of the tail lights and the the side marker filiments to get back to ground (if the marker lights are in fact grounded). In this case the brake lights would cease to appear to work if the running lights were turned on as there would be equal potential one each side of the filaments. One explanation I can come up with for the brake lights to appear to work and the blinkers not could be related to the impedance of the two parallel stop/turn/tail elements when the brakes are applied as opposed to the series nature of the circuit when the turn signal is applied. Parallel resistance subtracts while series resistance adds.

I still think you probably have a grounding issue. The above description is the best I can remember of what I have "figured out" on my own trailers. I'm sure there are some engineers out there that can correct some of my "theory"..............