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Towing Relay

karl2000

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When I got my 120, the towing socket had been cut off. I wired on a new socket, but nothing was live on it.

After some investigation, I discovered the trailer wiring harness had been disconnected from both of the rear lights. I reconnected that, and now onto the next problem.

The indicators now flash twice as fast as they should (same as when a bulb has gone!).

The towing indicator relay (see pic) is getting 12V on the red (UB+) and ground (31) is OK. The IL and IR pins go to 12V when the indicator(s) are on; and the OL and OR also go to 12V to power the rear indicator. That all sounds OK.

However I also get 12V on AL and AR (trailer indicators) even though there is no load on them. Its like its expecting a trailer then flashing fast because there is no trailer bulbs. Should the relay always be putting 12V to AL and AR even if theres nothing attached? If so, whats the real point of it - why not just join IL=OL+AL and IR=OR+AR? Is the relay buggered, or any other ideas?

I assume the fast flashing was the reason it was disconnected in the first place...

Thanks!
 

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Karl,

First is as you have put a new socket on have you checked the wiring and made sure no shorts? Sure you have, but worth asking.
Second what happens to your indicators when the relay is removed?
Third what happens when trailer is attached?
I’ve had good success using one of these Tester (external site) when I’ve had problems before.
See you are not far from me - if lockdown ever ends could lend you it.
 
Im sure you have but,...I'll ask anyway. Have you disconnected that relay and checked all the pin connectors on the multiplug. I ask because someone on here had one of those relays burn out, - in a big way.
Earth connections on trailer wiring can play all sorts of tricks too.
 
Karl,

First is as you have put a new socket on have you checked the wiring and made sure no shorts? Sure you have, but worth asking.
Second what happens to your indicators when the relay is removed?
Third what happens when trailer is attached?
I’ve had good success using one of these Tester (external site) when I’ve had problems before.
See you are not far from me - if lockdown ever ends could lend you it.
Yeh, those testers are invaluable, double ended for trailer and vehicle testing.
 
Karl,

First is as you have put a new socket on have you checked the wiring and made sure no shorts? Sure you have, but worth asking.
Second what happens to your indicators when the relay is removed?
Third what happens when trailer is attached?
I’ve had good success using one of these Tester (external site) when I’ve had problems before.
See you are not far from me - if lockdown ever ends could lend you it.
Thanks for that!

1) seems OK but I'll double check tomorrow!

2) the rear indicators stop - once the relay is out, there is no 12V path to them. If i remove the relay and short IL-OL and IR-OR they work again and flash at normal rate. Thats the state I've left it in at the moment, as its easier to remove the relay and short those pins than mess about removing the rear lights and disconnecting the harness.

3) No idea! Not got a trailer, just wanted to figure out what was going on with it really... #LockdownFiddle

Good point about the tester - I forgot about those, I've got on in the garage - I'll give it a go tomorrow! Thanks!
 
Im sure you have but,...I'll ask anyway. Have you disconnected that relay and checked all the pin connectors on the multiplug. I ask because someone on here had one of those relays burn out, - in a big way.
Earth connections on trailer wiring can play all sorts of tricks too.
Plug and wiring looks OK from what I can see - I ripped the back panel out for a good look too. Could be earth somewhere... I'll see what the tester says tomorrow.

So whats the point of these relays then?

Cheers!
 
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Plug and wiring looks OK from what I can see - I ripped the back panel out for a good look too. Could be earth somewhere... I'll see what the tester says tomorrow.

So whats the point of these relays then?

Cheers!
They take the additional load of trailer lighting, manage charging battery in caravan and keeping fridge cold, while on the move. When you switch off engine, the relay switches off power to these so the do not continue to draw power from vehicle battery and flatten it, making it a non starter. When you start engine relay switches back over as alternator is charging vehicle battery + satisfying other loads
 
Plug and wiring looks OK from what I can see - I ripped the back panel out for a good look too. Could be earth somewhere... I'll see what the tester says tomorrow.

So whats the point of these relays then?

Cheers!
As regards earth, with towing wiring this is normally the thicker white one, if this earth appears ok, you could always as a double check, either permanent or temporary, run another wire from there to another good earth point, I.e. another bolt/screw somewhere else. One of those testers is a great help, as you get lights on to tell if all connections ok. Any that don't light up when plugged in, points you immediately to that colour/ function wire to go straight to. The tester is powered by a 9v pp3 rectangular battery.
Good luck.
 
In my 90 series which is fairly similar in this regard, there are two relays - one for each indicator (L and R). Each relay coil has earth on one side, and the light feed from the car on the other. Each relay switch/contact has permanent +12v on one side and the other side is the output to the trailer loom.

If they are flashing twice as fast, you have the trailer and car indicators connected together. This isn't correct and they should go via the relay. The relay acts as a kind of 'repeater' for the trailer, but puts minimal load on the car so doesn't affect the flash rate.

Let me know and I can draw a diagram if you like and show you the relays in mine. Only the indicators are like this the rest of the lights just hook onto the car's lights, old school style.

It's important to make sure the +12v for the relays is a permanent live, not switched, these are used for hazards too remember and you want to be able to operate these with no key in.

AFAIK there are no factory relays for trailer's battery etc. Certainly on my 90 there aren't.
 
Any luck with the tester?

It’s always a worry when there’s been modifications by someone else as you are never 100% sure what they’ve done. Not having the socket on seems a bit of a bodge, but also water ingress could have got into the exposed cable and all sorts of issues can be had - especially earth problems (which are nearly always the issue with towing accessories).

If the worse come to the worse then I’d replace the trailer plug loom, it’s easy to do. See Genuine Toyota loom (indicators in bumper) [external site]
 
Any luck with the tester?

It’s always a worry when there’s been modifications by someone else as you are never 100% sure what they’ve done. Not having the socket on seems a bit of a bodge, but also water ingress could have got into the exposed cable and all sorts of issues can be had - especially earth problems (which are nearly always the issue with towing accessories).

If the worse come to the worse then I’d replace the trailer plug loom, it’s easy to do. See Genuine Toyota loom (indicators in bumper) [external site]
Earth can be aproblem as said earlier.
 
All interesting,
On both my 120s i fitted a 3rd party towbar and everything worked perfectly but when a trailer is hooked up the lights falsh twice as fast!
Never looked into this but sounds interesting, 2 differnet 120s with the same quirk.
I would gues that its because the relay works on a certain current passing through it and when extra lights are applied then this will essentially change it?
Also noted that it doesnt change the speed when LED lights are applied only traditioponal ones!

Simon
 
Again interesting. My 120 with i assume, dealer fitted Brink/ Toyota branded towbar and all the neccessary wiring looms and that same red voltek relay, came to me with damaged socket, so i replaced it.
Hooked up to my twin axle trailer indicators flash normally, there are extra running lights on trailer, bu I don't see that as making a difference as a different circuit. Haven't tried on caravan yet.
 
Quick update after some more investigation.....

Plugged in a tester; two problems:

1) the light came on for Left Indicator (yellow wire) even though nothing was turned on.

2) fog light indicator wouldn't come on. (Not too worried about this at the moment; I know they're on a separate cable; maybe they've been unplugged too? wlll investigate)

Everything else seemed OK.

Checked the voltage between yellow (AL) and ground (31) on the relay and got 3.921 volts - see attached.

Voltage between AR and ground was 0 as I'd expect.

So I think that points to the relay being knackered? With the relay unplugged, voltage yellow to ground is 0V.

Thanks for your input!
 

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Quick update after some more investigation.....

Plugged in a tester; two problems:

1) the light came on for Left Indicator (yellow wire) even though nothing was turned on.

2) fog light indicator wouldn't come on. (Not too worried about this at the moment; I know they're on a separate cable; maybe they've been unplugged too? wlll investigate)

Everything else seemed OK.

Checked the voltage between yellow (AL) and ground (31) on the relay and got 3.921 volts - see attached.

Voltage between AR and ground was 0 as I'd expect.

So I think that points to the relay being knackered? With the relay unplugged, voltage yellow to ground is 0V.

Thanks for your input!
You have not got LED Lamps in the rear of the car?
 
Karl2000, cant help with that particular problem, but you've got me thinking now, without digging mine out of garage and trying, shouldn't the individual series of lights come on if the systems check out, or they only come on if there is a fault ?. Sorry can't remember, probably confused you now !
 
Karl2000, cant help with that particular problem, but you've got me thinking now, without digging mine out of garage and trying, shouldn't the individual series of lights come on if the systems check out, or they only come on if there is a fault ?. Sorry can't remember, probably confused you now !
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!
 
Right, just checked instructions on line for mine, I should imagine they're all pretty much same.
It confirms what I thought, with nothing turned on, indicators on tester, light up if bulbs and wiring are good.
Going by that all that's good on yours is only the yellow wire, left hand indicator.
I can't remember if you had replaced the socket on vehicle or not, but check wiring in there is good /in right
places, if not replace socket. Because of location of socket, corrosion can set in, even if not visible, ie inside the little brass bit where wire is secured. At times I have backed off screws and retightened, or removed wires, snipped off discoloured wire ends and 're made joints. If any thing in there looks iffy, replace socket in which you will be remaking those joints anyway.
Before you start panicking about readings (me) do those checks, personally that's easier for me than taking readings and trying to interprate. Good luck.
 
All interesting,
On both my 120s i fitted a 3rd party towbar and everything worked perfectly but when a trailer is hooked up the lights falsh twice as fast!
Never looked into this but sounds interesting, 2 differnet 120s with the same quirk.
I would gues that its because the relay works on a certain current passing through it and when extra lights are applied then this will essentially change it?
Also noted that it doesnt change the speed when LED lights are applied only traditioponal ones!
Simon
LED trailer lights draw a lot less current than tungsten ones, and the flasher is dependent on load. So if you use LED lights this doesn't add too much to the usual 'car' load of three lamps. If you use tungsten trailer lights then it does add a significant amount more, and causes the flasher to flash faster. The flasher works by passing the lamp current over a bi-metallic strip. This strip heats up and bends away making the 'flash'. So more load means it heats up faster and flashes faster.

Unfortunately the only way round it is to add a couple of relays (like LED lamps these add negligible load), and use these to 'repeat' the indicators. The trailer can then draw whatever it likes without affecting the flash rate. The factory Toyota towbar loom includes these repeater relays.
 
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