Wiring a Towbar 12 N socket with 7 way Bypass Relay

This job requires work on the vehicles electrics and might void your warranty And if done incorrectly could start a Fire

thats the disclamer out of the way

Gone are the Days when you'd just scotch hook the trailing end of the 7 way cable to the loom with the bulb failure system and Fiats notoriously small cables it cant be done for fear of melting the loom and having the check Bulb light come on every time you use the socket....

you dont need a towbar to always need road lights if you use a strap on cycle rack for example that blocks vision of your road lights you will need a light board for example..

I have left out the towbar bracket fitting instructions as these are specific to the brand of towbar you have bought

The stuff you will need are
12N socket and mounting hardware
2 mtrs of 7 core wire
1.5 to 2 mtrs of 2 core twin 1.5mm is fine
a Reel of Single core 20Amp rated cable
7 scotch hooks
7 Way Bypass relay
a blue eyelet crimp
Fuse holder and associated spade crimps
Soldering iron,
Screwdriver,
wire cutters,
stanly knife
wire strippers
insulating tape
Cable ties..
A working lighting board is handy to test
I think thats it......

johnson550 · 05-07-2008

if I am reading this correctly you have a 20amp fuse inline with 20amp wire in the event of a short will the wire not melt at the same time as the fuse

**Andy Monty** · 19-08-2008

Originally Posted by johnson550

if I am reading this correctly you have a 20amp fuse inline with 20amp wire in the event of a short will the wire not melt at the same time as the fuse

bad wording on my part should read something like a cable able to take in excess of 20A

happy now

Jimbo34 · 21-08-2008

I have never wired a towbar on a Fiat but have done several Citroen Xantias.

If you are towing a caravan with loads of electrical loads etc, I can understand the need for a 20+ Amp wire. And even that seems huge.

I however will be using my old Multipla for a bike rack and small trailer for taking rubbish to the dump...

I cant believe that an extra bulb on each circuit in the loom from the light board is going to melt it ! The load is tiny...even on a cheapo loom...

I don't recall there being a blown bulb function on the 2002 Multipla either but I could put up with that if it came on. It would go nicely with the airbag light, I can't get that blighter to go out either.

Feel free to enlighten us further as I feel that you have done a top notch, belt and braces job that can handle everything. I am holding back now as I am more of a grease monkey than an electrician and you have got me worried.

**Andy Monty** · 18-06-2009

Originally Posted by Jimbo34

I have never wired a towbar on a Fiat but have done several Citroen Xantias.

If you are towing a caravan with loads of electrical loads etc, I can understand the need for a 20+ Amp wire. And even that seems huge.

I however will be using my old Multipla for a bike rack and small trailer for taking rubbish to the dump...

I cant believe that an extra bulb on each circuit in the loom from the light board is going to melt it ! The load is tiny...even on a cheapo loom...

I don't recall there being a blown bulb function on the 2002 Multipla either but I could put up with that if it came on. It would go nicely with the airbag light, I can't get that blighter to go out either.

Feel free to enlighten us further as I feel that you have done a top notch, belt and braces job that can handle everything. I am holding back now as I am more of a grease monkey than an electrician and you have got me worried.

just to do a bit of basic maths....

v=I/R

I/V=R

example

180 Watt on a 12v circuit = 15A

now for a lighting board,

2x21watt (hazards/indicators) 42W
2x21 watt (rear brake lights) 42w
2x 10Watt (side lights) 20w
2x 21watt (fog lights) 42w
= 146W

and on a caravan and some trailers it will probably have in addition

2x10W festoon bulbs for the number plate lights

2= side marker lamps 2x10w

and 2 front marker lamps 2x5w

giving 176W max draw giving 14.6A pull

giving you close to a 5A safety margin

and if you want to be really picky add on a 21w reversing light and high level brake lamp on newer caravans...

now you could argue that you will never have all the lights on at once so just imagine you brake down on the motorway in Fog as you pull onto the hard shoulder your braking to slow and switch on your hazard lights.............

planetmalthus · 23-09-2009

Thank you for this post. I needed someone to tell me that the alarm noise going off every time I indicate is a good thing. I'd been worried that I had seriously buggered it up.

**T14086** · 23-09-2009

Originally Posted by planetmalthus

Thank you for this post. I needed someone to tell me that the alarm noise going off every time I indicate is a good thing. I'd been worried that I had seriously buggered it up.

Its supposed to, legal requirement either audible or visual warning.

**Andy Monty** · 26-09-2009

Originally Posted by planetmalthus

Thank you for this post. I needed someone to tell me that the alarm noise going off every time I indicate is a good thing. I'd been worried that I had seriously buggered it up.

no problem mine was overly loud so i have shoved a foam ear plug in the sounder hole not silenced it completely ((as i want to know the indicators are working)) but its less harsh

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