Tail lights on trailer working intermittently

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

WhenI plug my trailer into my car, sometimes the tail lights work and sometimes they don't. When they don't I can hear a buzzing sound coming from the back of my car.

I am thinking this might be a relay for the tow plug?
If it is a relay, is this something that I can replace myself or is it an auto electrician job?

It's a real pain as all the lights will work fine, then the next time I plug it in, no tail lights?

Cheers,

Mark

[peter_mcc Senior Member Find all posts View Profile Close peter_mcc]

If you look in where the jack is there should be a small (10cm x 5cm ish) black box stuck to the car with a cable harness coming in the bottom. This "drives" the trailer lights. Next time you hear the buzzing perhaps check if the sound is coming from it.

At least that's what the Toyota tow bar has... if you have a different one it might be wired another way.

[Hally Senior Member Find all posts View Profile Close Hally]

Check the pins in the plug both sides.
My CT pins were closed in a bit so would work sometimes when pluged in to prado but when pluged into my other car was fine just simply spread the pin open.

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

Thanks Peter,

I just had a look, I do have the Toyota tow bar and the loom from the trailer plug heads up into the jack compartment.
However I can't see any black box.

I'll have a play tomorrow after work or on the weekend to see if I can get it buzzing :-)

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

Check the pins in the plug both sides.
My CT pins were closed in a bit so would work sometimes when pluged in to prado but when pluged into my other car was fine just simply spread the pin open.

I'll have a look Hally.
It was doing it with the original Toyota plug on the car so I replaced it with a new utilux one and it's still doing it.

Though thats not to say the female portion of the trailer plug isn't a bit loose on that pin.

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

I have a Reece style bar fitted by Vic Park Towbars utilizing the Toyota harness. You should be getting a solid tick tock sound from the rear relay that was detailed above. If it's buzzing then the relay is shot. It's there, towards the rear of the car in that jack compartment.

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

I'll have another look in the jack compartment, but I couldn't see anything when I looked earlier.

Assuming it is a buggered relay, which I suspect, do you know if it is something that is easily replaced of is it a trip to the auto electricians?

[AussieAndy Find all posts View Profile Close AussieAndy]

It's a control module (basically a box of relays). Not sure if anyone else has had any luck finding a replacement. Lumen is the company who make the towbar loom for Toyota so they may be able to help you out.

[Fred63 Advanced Member Find all posts View Profile Close Fred63]

i had a similar problem in another car.
Turned out to be an intermittent short circuit in the wiring.
The control module had overload / Short Circuit protection built in. the Toyota one may be the same.
Easy test for the wiring check resistance with a meter and get someone to move the wiring around while watch the meter to see if it changes.
Second way connect power to the taillight pin with a 5A inline fuse all lights working, then try pulling and moving the wiring around to see if there is a short circuit the fuse will blow.
if not then your back to the control module

[wv1 Junior Member Find all posts View Profile Close wv1]

I'll have another look in the jack compartment, but I couldn't see anything when I looked earlier.

Assuming it is a buggered relay, which I suspect, do you know if it is something that is easily replaced of is it a trip to the auto electricians?

Mine is not in the Jack compartment but in a space next to it, where Toyota recommend mounting it. From memory you have to remove the side trim to access it.

[Bushbasher Out of control poster! Find all posts View Profile Close Bushbasher]

I meant in the void between the jack compartment and the rear panel, basically under the tail lamp. I can't get to mine easily because of the drawers.

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

Just had a look and using a mirror I can see it up near the tail light.

I'll have a look tomorrow, that is plug trailer in and have a listen. I'll need to remove my draw to actually get to it though :-(
I can't not have tail lights on the trailer so should be a fun Saturday L0L!

[LeighW Avid PP Poster! Find all posts View Profile Close LeighW]

Generally those sorts of things a pretty reliable, when it comes to trailers I would carefully
check the trailer plugs sockets for faulty wiring, and the trailer itself as it is more likley to be
a faulty in the wiring than the module. If possible can you borrow another trailer to see if you
have the same issue?

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

Generally those sorts of things a pretty reliable, when it comes to trailers I would carefully
check the trailer plugs sockets for faulty wiring, and the trialer itself as it is more likley to be
a faulty in the wiring than the module. If possible can you borrow another trailer to see if you
have the same issue?

Thanks Leigh,

I'll see about connecting to another trailer.

I'd like to think the trailer wiring is good as I built the trailer myself I did all of the wiring making sure all joins are soldered and adhesive shrink tube covers all the joins. However I won't rule anything out at the moment!

The thing that is doing my head inn is I've just spent nearly an hour trying to get it not to work so I can test a couple of things but all is working fine.

However I on Wednesday I took it to get weighed, check the lights before I left and all was fine, got home and no tail lights.
Unplugged and plugged the trailer in a couple of times and it was working again, then get ready for its inspection Thursday and no lights so I had to cancel the inspection :-(

I'd be happy if it would just simply work or not work so I could get on with it!

[Westcoast Mark Member Find all posts View Profile Close Westcoast Mark]

So, I have found the source of my problem and thankfully it is not with the car, however I am still a bit confused.

Because the trailer has a hard wired earth through the plug I haven't had the trailer physically attached to the car today and all of the lights have been working.
I hooked it up tonight with the intention of driving around the block to see if that did anything, and bingo! No tail lights. Dis-connected the tow hitch and the tail lights come back on.

So why is it doing this and only with the tail lights?

Cheers,

Mark