I managed to get round to fitting my towbar today but got a bit scared when it came to the electrics. I've got a 7 pin plug that's wires into a relay and then to the source. Is it a fairly simple process or should it be left to the pros?
It's on a 2012 vauxhall astra sports tourer.
Can I take a power source off the boot light or boot cigarette lighter to save running a cable all the way to the front of the car? Obviously fuse it from there to the relay box supplied.

No need to run power.

You need indicators, side light, brake light x 2, fog light, reverse light and earth IIRC.

you can see what light does what in the rear cluster and trace it to the loom then scotch lock onto it.

I would use a powerprobe an solder it on ideally but i guess you dont have these. Its easy.

You will probably need power if it's a bypass relay.

Yes it's a bypass relay and requires power. Also I have 2 tail lights on each side so do I only have to connect to 1 or both on each side.

Check if the car has a REC. I have a 2010 zafira, bought a used towbar with full wiring including the box of tricks so it plugs direct into the REC (big black box on the NS rear wing behind a trim panel)
Seems some cars have tricky bits, especially with reversing sensors and all the extra warning lights and so on. I plumped for the plug and play option....

i think i'm right in saying with a bypass relay the 12v power feed is what actually feeds the trailer lights.
for that reason i would take it back to the battery rather than taking it from elsewhere.

It does have a second fuse board in the boot behind a panel. I believe this is for the plug and play towing kit that vauxhall do, problem is it costs a lot of money. I don't need anything fancy just a simple light board on the trailer to tow my kit car.

You probably need to find a permanent live in at the rear to ensure things like side lights and hazard indicators work all the time on the trailer board.

Thanks. I've just done some reading online and all seems simple enough. I'll have to check the rear cigarette lighter to see if that's permanently live or not, also need to buy some wire to run from one side of the car to the other. I think the wires for lighting ect is 32 gauge?

I think you will need a car specific loom for the astra! It could screw up the lights out sensors in the ecu or whatever deals with that? I fitted a towbar for a mate on an astra with the REC in the boot, it was easy as plugging it in. 1 big plug, it is a fair bit of money for the wiring but don't go to vauxhall. My mate got his off ebay for about £70. If it needs anything turning on with Opcom I've got that, as long as you have your car's pass card it should be easy. My mates worked without doing anything!

[Edited on 30/1/15 by melly-g]

Thanks for the advice. It seems a few people have been successful as long as a bypass relay is used. The cheapest I found the specific wiring was £90 which is a fair chunk, I suppose I can try what I have out and go from there.

My Passat has a cubby hole that used to have a first aid box in there, now long gone. Next to it is a double
auxiliary power point, (mustn't call them *** or I might get sued because little Jimmy read this post and went
straight down the pub and bought 20 Woodbines) so it would be rude not to use it.


VW B5 tow bar wiring


The 7 way bypass relay and in-line fuse (to the left) cost under £20 and the wires to the right go to the rear light unit.
It seemed a better way than those horrible ScotchLoks. A couple have to go to the other side rear light unit.


Putting it in the cubby hole has another advantage. I can hardly hear the annoying beep from the indicators. Result.


Paul G

I do seem to have power at the back, cigarette lighter, boot light and also the rear fuse box. I'm a bit paranoid to use any of these as I've heard it can sometimes upset the car electrics as that power also is connected to the rec and canbus.
It's been advised just to run a fresh cable straight to the battery and fuse it that way the light board will have its own designated power supply.