Towing Relay

[Tractionman]

Don't worry, doesn't take much to confuse me mate!

On my tester, the light comes on if it gets a voltage between ground and the particular pin; i tested the tester first by putting 12V across each pin and watched each light illuminate.

When I turned the lights on, or flashed the hazard lights or indicators, the correct lights on the tester lit up. But when everything was off, the left indicator light on the tester was illuminated, because of that 4V or so voltage that I can't explain except maybe a bad relay.

BTW I took the cover off the relay and it looks fine, nothing obviously burnt or damaged.

Does anyone else have a voltage between yellow and white on that relay, when the indicators are off? I assume not!

Thanks!

Karl2000, went out earlier this am and did a double, double check. I plugged in the trailer light tester, held the yellow button in (as required), all lights come on indicating all is good. Then plugged in a trailer board from the garage, All lights function and flasher rate normal, as on seperate trailer. That leads me to the conclusion I had earlier, that your one light indicated is the only wiring correct, there is a problem with the rest.
The problem must lie within and/or including the socket.
Has anyone 'modified' the Toyota loom at the rear end connections with scotchlocks, they can be a constant source of problems, especially when exposed.

 

[karl2000]

Karl2000, went out earlier this am and did a double, double check. I plugged in the trailer light tester, held the yellow button in (as required), all lights come on indicating all is good. Then plugged in a trailer board from the garage, All lights function and flasher rate normal, as on seperate trailer. That leads me to the conclusion I had earlier, that your one light indicated is the only wiring correct, there is a problem with the rest.
The problem must lie within and/or including the socket.
Has anyone 'modified' the Toyota loom at the rear end connections with scotchlocks, they can be a constant source of problems, especially when exposed.

Thanks for that mate, I appreciate it.

My tester looks like the one in this video:

No idea what he's saying, but you can see it working!

Note that I didn't push the button on my tester - mine says 'Push yellow button only when checking trailer function' - which I took to mean its not needed when checking the car side?

I took the connector off yesterday, re-stripped the wires, checked them for continuity/low resistance to the other end of the loom and refitted a new socket. I'm seeing 12V on all the trailer socket pins where I'd expect it (apart from fog lights... will get to that!). I still suspect the relay - that 4V between yellow and white doesn't seem right to me, and it only appears when the relay is plugged in so I don't think its the wires.....

 

[Tractionman]

Thanks for that mate, I appreciate it.

My tester looks like the one in this video:

No idea what he's saying, but you can see it working!

Note that I didn't push the button on my tester - mine says 'Push yellow button only when checking trailer function' - which I took to mean its not needed when checking the car side?

I took the connector off yesterday, re-stripped the wires, checked them for continuity/low resistance to the other end of the loom and refitted a new socket. I'm seeing 12V on all the trailer socket pins where I'd expect it (apart from fog lights... will get to that!). I still suspect the relay - that 4V between yellow and white doesn't seem right to me, and it only appears when the relay is plugged in so I don't think its the wires.....

Yeah, mine looks same, didnt have any info about only press button for trailer, so I pressed anyway.
Interestingly, all lights on tester lit as said, and trailer previouslyworked properly and now the light board in garage works properly. Going by that result, every thing I've done pans out. This is wierd.
What further confuses me is, how you are getting 12v on certain pins in socket, there should be no direct 12v feed in there.

 

[karl2000]

Yeah, mine looks same, didnt have any info about only press button for trailer, so I pressed anyway.
Interestingly, all lights on tester lit as said, and trailer previouslyworked properly and now the light board in garage works properly. Going by that result, every thing I've done pans out. This is wierd.
What further confuses me is, how you are getting 12v on certain pins in socket, there should be no direct 12v feed in there.

But if you turn the lights on, you'll get 12V right? So if the rear lights are on, I'd expect (and get) 12V between brown (right) and white (earth); and between black (left) and white (earth). Obviously if lights are off, there shouldn't be anything? (Except my damn 4V between yellow and white!)

 

[Tractionman]

But if you turn the lights on, you'll get 12V right? So if the rear lights are on, I'd expect (and get) 12V between brown (right) and white (earth); and between black (left) and white (earth). Obviously if lights are off, there shouldn't be anything? (Except my damn 4V between yellow and white!)

Correct, sorry thought you had nothing on.
Just for clarity, mine, been out again.
Plugged tester in lc, no lights come on until I press button,
Plugged tester in ĺight board, no lights come on until I press button,
Plugged tester in trailer, no lights come on until I press button,
Plugged trailer directly into lc and all road lights, indicators etc, function as normal ,
So as my trailer lights all operate correctly when hooked up, it appears the checks I did with the tester are correct, and it is operating as it should.
Agreed you should not be getting reading across yellow l/h indicator and white earth if not on.
As there is no direct feed into the socket, only when you switch on lights indicators etc, that suggests as you have already deduced, the yellow is drawing power from somwhere, and that is probably key to the problem.
From behind the rear bumper can you and unplug the l/h indicator in the towing loom, to isolate it from the main loom, then at that spot in the main loom use your multimeter, to see if there is that 4v, if not, with the l/h indicator and ignition on check again and see if there is a pulse reading as it 'flashes'. If both those comes up good, the problem lies within that towing loom and/or tow plug. A process of elimination really.
to check if you have a reading

 

[karl2000]

Correct, sorry thought you had nothing on.
Just for clarity, mine, been out again.
Plugged tester in lc, no lights come on until I press button,
Plugged tester in ĺight board, no lights come on until I press button,
Plugged tester in trailer, no lights come on until I press button,
Plugged trailer directly into lc and all road lights, indicators etc, function as normal ,
So as my trailer lights all operate correctly when hooked up, it appears the checks I did with the tester are correct, and it is operating as it should.
Agreed you should not be getting reading across yellow l/h indicator and white earth if not on.
As there is no direct feed into the socket, only when you switch on lights indicators etc, that suggests as you have already deduced, the yellow is drawing power from somwhere, and that is probably key to the problem.
From behind the rear bumper can you and unplug the l/h indicator in the towing loom, to isolate it from the main loom, then at that spot in the main loom use your multimeter, to see if there is that 4v, if not, with the l/h indicator and ignition on check again and see if there is a pulse reading as it 'flashes'. If both those comes up good, the problem lies within that towing loom and/or tow plug. A process of elimination really.
to check if you have a reading

Thanks for that, that makes sense.

I did some of those checks yesterday when I had it all in bits. That yellow wire is the output from the relay (AL I think) and doesn't go anywhere else - it just runs straight from the relay output to the towing socket. 4V when the relay is plugged in, 0V when its taken out. So I think that points to a dodgy relay....

I've got one coming tomorrow (hopefully!) so we will find out shortly....

 

[Tractionman]

Thanks for that, that makes sense.

I did some of those checks yesterday when I had it all in bits. That yellow wire is the output from the relay (AL I think) and doesn't go anywhere else - it just runs straight from the relay output to the towing socket. 4V when the relay is plugged in, 0V when its taken out. So I think that points to a dodgy relay....

I've got one coming tomorrow (hopefully!) so we will find out shortly....

Well done mate.

 

[AdventureWagon]

Would just say if you are checking with a digital multimeter don't worry too much about stray voltages here and there - DMMs have a very high input impedance (resistance) meaning they will see any tiny potential for its true voltage. Whereas a bulb has a very low impedance(resistance) and will immediately kill these stray voltages. If the earth point for the trailer plug on the vehicle or trailer is compromised you will see stray voltages like this.

Best way to test the output is with a light bulb connected to earth at one side - that's all you care about at the trailer plug - DMM is fine for fine troubleshooting once you have a suspected culprit though.

 

[AdventureWagon]

And also remember a crap connection can appear fine on a DMM (especially with the continuity beeper) but then not work for bulbs etc. Continuity beepers usually still go off at up to 50 ohms. Even 10 ohms is a very poor connection for tungsten lights, perfectly fine for some electronics but will buzz out fine on a DMM.

 

[karl2000]

Would just say if you are checking with a digital multimeter don't worry too much about stray voltages here and there - DMMs have a very high input impedance (resistance) meaning they will see any tiny potential for its true voltage. Whereas a bulb has a very low impedance(resistance) and will immediately kill these stray voltages. If the earth point for the trailer plug on the vehicle or trailer is compromised you will see stray voltages like this.

Best way to test the output is with a light bulb connected to earth at one side - that's all you care about at the trailer plug - DMM is fine for fine troubleshooting once you have a suspected culprit though.

Good point that, thanks! Originally the light lit up on the trailer tested which pointed me to that; and also my test light (the screwdriver type thing with a negative lead and a point on it) lit up but was dim, so I dont think it was a ghost voltage in this case! But hopefully will find out more today.....

 

[karl2000]

And also remember a crap connection can appear fine on a DMM (especially with the continuity beeper) but then not work for bulbs etc. Continuity beepers usually still go off at up to 50 ohms. Even 10 ohms is a very poor connection for tungsten lights, perfectly fine for some electronics but will buzz out fine on a DMM.

Thanks for that - those numbers are useful for future reference. in this case I think it was OK - when I checked it, they were all less than 0.5 ohms.

 

[karl2000]

Update - new relay in, and it now works! Thanks for the pointers and advice.

 

[Tractionman]

Update - new relay in, and it now works! Thanks for the pointers and advice.

Oh yeah, you is da man. Job well done.

 

[Tractionman]

Update - new relay in, and it now works! Thanks for the pointers and advice.

Karl, out of interest and maybe for further use, which relay did you change. The big red one in the back ?

 

[karl2000]

Karl, out of interest and maybe for further use, which relay did you change. The big red one in the back ?

Yep thats the one mate - the red SIK indicator relay!

 

[Tractionman]

Thanks, karl