You have either an earthing problem on one or both (if a common earth) of the rear light clusters almost certainly caused by damp/water ingress or possibly within the towing socket, your going over it with the power hose will have either caused o exacerbated it.

 

The bypass relay module will click the relevant relay (there are 6 or 8) when a voltage is detected on that circuit, earth problems will cause backfeeding of voltage to the other circuits, the relays will always click when switching on and off but are usually inaudible, at least to my old ears, no idea why it should have chosen now to become more audible, perhaps the feed to the relay had been disconnected before or had a bad connection, who knows.

 

In any case you need to check the earths at the rear, the connections to the towing socket and relay and finally the relay operation, there should be an audible "beep" when the indicators are used if a trailer is connected, its not a click and should not be happening if you do not have trailer lights connected but anything could be happening with bad earths and water.

 

Most bypass relays will function even when a trailer/caravan lighting plug is not inserted, the audible "beep" should only occur when inserted and if the trailer/caravan indicator light is functioning. I cant hear mine when in motion with the rear seats up.

Edited 19 October, 20205 yr by J.R.

Thanks - the tow bar guy has just called me.  He said that it always makes this click sound i.e. even when not connected.  (There is an indicator "dinging" sound only when the socket is connected.  However he said he'd come and take a look......?  It's completely stumped me as I'm pretty much 100% certain I haven't heard this clicking (when touching the break peddle) before Friday.  I'll let you know what happens when he's been out.  Thank you again for all your help - really appreciated it. 

That corresponds with my suggestion that it was not working before, I cant see what someone fitting brake pads could do to bring it back to life but if they had to disconnect the battery or remove any fuses then they might.

 

When I got my car I found a badly bodged connection to the battery leading into the entrails of the vehicle, I disconnecetd it and waited to see what stopped working, nothing did and I completely forgot about it.

 

A year later Ihooked up my trailer and the lights did not work, checked back to the relay and found it was unpowered, traced the wire back through the door sill trims, through the bulkhead to under the bonnet to find it was the cable that I had disconected.

 

Be aware that the relay you have can significantly increase the parasitic battery drain, mine are all now switched so only draw current when I want them to.

Thank you for this, really helpful.  Something I noticed when last week I was having an MOT done - they put the hazard lights on whilst they jacked the car up and left them on for about 1/2 an hour.  Have no idea if this could be connected to anything and I can't think why it would but to my mind, the clicking in the relay sound is a new sound so something may have triggered it to start working very recently.

14 hours ago, Wildman said:

Thank you for this, really helpful.  Something I noticed when last week I was having an MOT done - they put the hazard lights on whilst they jacked the car up and left them on for about 1/2 an hour.  Have no idea if this could be connected to anything and I can't think why it would but to my mind, the clicking in the relay sound is a new sound so something may have triggered it to start working very recently.

 

I dont know if relays can suddenly get noisier but one option is to replace the relay and see if a newer one is quieter.

Otherwise could you maybe put something over the relay to try and deaden the sound somehow as a test and see if its then quiet enough?  Ive got an aftermarket bar on mine and the relays are in the boot side cubby hole and Ive got seat covers, cloths, couple of dog towels and all sorts rammed in there.

 

Im not aware the relays produce heat or if they need ventilation - maybe someone else can advise.

Funnily enough - that's exactly what the guy who installed my towbar has suggested and has even offered to come down to do for no charge.  Just in case anyone needs a towbar, this guy Mark and his son are really decent guys who do a fantastic job and then go out of their way to follow up & make sure you're happy.  He's called Towbar Man (South) and is based in Alton.  Thanks again.