Tow bar wiring problem.

[bern]

I'm fairly handy with a set of spanners but fairly incompetent with wires!

I have a new to me '04 legacy estate. It came with an Alko detachable tow bar and twin electric sockets. Yesterday I bought a tow bar mounted bike rack and here the issue starts.

When I plug the rack in and turn either indicator on they flash twice as fast as normal, like when you have a faulty bulb. However if you turn the hazards on they both flash at the normal speed.

I unplugged the rack and tested the pins in the socket with an test lamp. With either indicator in if you touch the respective pin the test lamp flashes at the correct speed with the car indicator bulb, however if you touch the opposite side indicator pin (in effect earthing it) you get the double flashing speed.

Today I've stripped the socket hoping to fine something obvious like a broken or loose connection but everything seems in good order. I've had the rear lights out to check the looms and they all look ok.

Any help much appreciated.

[smokey mow]

Sounds like whoever wired in the towbar electrics didn’t fit the relay

[bern]

Cheers, where / how would this relay be wired in?

I'm assuming due to the twin electrics and the Alko hitch that it has been used to pull a caravan at some point. So I would also assume that it worked correctly at some point as well.

But you know what they say about assume!

[Etretat]

Not played with car electrics for many years, Canbus sounds like it makes DIY impossible, but an 04 car may not have it.
I fitted towbars and electrics to a number of cars back in the day. The indicator relay has to be replaced with one suitable for towing otherwise the rapid flashing would be the result. In addition it used to be a legal requirement to have an additional warning light which would flash when the indicators were used with the trailor connected.
HTH

[Spare tyre]

I’d start by removing the indicator bulbs from the rack and then trying and see what happens

If the same remove all bulbs from the rack and try again


I’d also see if anyone else has a trailer you can try or try your rack on a different car

Final check, not led bulbs involved anywhere ?

[Spare tyre]

Etretat said:

Not played with car electrics for many years, Canbus sounds like it makes DIY impossible, but an 04 car may not have it.
I fitted towbars and electrics to a number of cars back in the day. The indicator relay has to be replaced with one suitable for towing otherwise the rapid flashing would be the result. In addition it used to be a legal requirement to have an additional warning light which would flash when the indicators were used with the trailor connected.
HTH

Not sure on the additional flasher

My fathers car and my car both have dealer fitted tow bars, they beep but no additional flashers

[vikingaero]

Erm, isn't this normal.

Hazards gives the standard click-click sound.

When something is plugged into the tow bar electrics and you indicate, you get the double-frantic click to remind you that you are towing a 500ft trailer (or just a bike rack).

[Spare tyre]

vikingaero said:

Erm, isn't this normal.

Hazards gives the standard click-click sound.

When something is plugged into the tow bar electrics and you indicate, you get the double-frantic click to remind you that you are towing a 500ft trailer (or just a bike rack).

I think the op is reporting externally the lights are flashing quicker

If you can lice with it, it might actually be within the required flashes per minute range anyway

[bern]

Spare tyre said:

vikingaero said:

Erm, isn't this normal.

Hazards gives the standard click-click sound.

When something is plugged into the tow bar electrics and you indicate, you get the double-frantic click to remind you that you are towing a 500ft trailer (or just a bike rack).

I think the op is reporting externally the lights are flashing quicker

If you can lice with it, it might actually be within the required flashes per minute range anyway

This is true. They flash at double the rate. I haven't had time to investigate further. But will report back when I do.

[anonymous-user]

Etretat said:

Not played with car electrics for many years, Canbus sounds like it makes DIY impossible, but an 04 car may not have it.
I fitted towbars and electrics to a number of cars back in the day. The indicator relay has to be replaced with one suitable for towing otherwise the rapid flashing would be the result. In addition it used to be a legal requirement to have an additional warning light which would flash when the indicators were used with the trailor connected.
HTH

Canbus isn't a problem. You still tap into the wires that go to the lights. Just now you use a relay module - a small box that each light signal goes into, plus 12v from the battery, then it outputs the relevant power to each light, using the source feeds purely as a signal/trigger and pulling the actual light power direct from the battery. Basically a small box with 5 or 6 relays in it that can also handle rear lights that have only one wire serving both brake and tail light. Less than £10. They beep too. A dash light isn't law.

An expensive example. eBay links seem to be crazy long these days.

https://www.amazon.co.uk/Ring-Smart-Logic-Bypass-R...