Towbar electrics wiring (relay bypass, not genuine)

[Arctra]

Hi guys

So I finally got around to installing my towbar electrics that I got from Towbars Direct (Towbars Direct | Witter Towbar Systems, Tow-Trust Towbars, Westfalia Automotive, Thule Towing Systems (Brink), Bosal, GDW, PCT Automotive, Westfalia Monoflex, Westfalia SIARR) in the UK. I ordered the "Single Electric Kit (12N) with Multiplex By-Pass Interface Relay" for just £26.45. They won't ship to Australia, so I had them ship to a mate who then forwarded it to me. Ended up costing me a total of about $50 for the unit and getting it sent to me - BARGAIN!



I was pretty worried about doing the wiring and getting the scotch locks on properly and onto the correct wires. Thankfully I had access to Elsawin so I could check up on which wires were the correct ones to tap. Removing the rear lights is very simple if you have a torx screwdriver set to remove the 2 screws holding each light in. There is a 4 pin plug that has 2 catches on it that you need to release the plug from the light units.

On the right hand side I tapped 3 of the wires. The plug has numbered pins to make things easier, as well as the colour coded wires. On the right hand side they are as follows:
Pin 1 - Black and Yellow - Tail light
Pin 2 - Black and Green - Right Indicator
Pin 3 - Black and Purple - Brake light
Pin 4 - Brown - Earth



On the left hand side I only tapped 1 wire - the indicator. On the left hand side the wiring is as follows:
Pin 1 - Brown - Earth
Pin 2 - Black and Red - Brake light
Pin 3 - Black and White - Left Indicator
Pin 4 - Black and Yellow - Tail light



Testing the above wiring my tail light (when lights are on), brake light (when brake pedal is depressed), and left and right indicators work perfectly. I don't have reverse lights or side lights on my little trailer so haven't bothered trying to wire them yet. I probably should at some stage, but I am happy for now. At the moment I am powering the unit off the 12V supply in the boot - again, I'll investigate alternative options at some stage but for now I am happy.

Hope those of you that are looking for an alternative find this useful. it's cheap and it works. Of course, it does not have the trailer stability program that the OEM wiring harness does, so the caveats that go with that apply if you go this route. I have a tiny little motorcycle trailer so don't feel I need it.

[*thad*]

Now that you have confirmed it works please remove those horrid scotch locks and solder the wires on! If traveling on rough road it will give you problems in the end. If not at least wrap them in electrical tape.
Other than that good to know cheers.

[mikinoz]

So cheap, so simple.

[Arctra]

Now that you have confirmed it works please remove those horrid scotch locks and solder the wires on! If traveling on rough road it will give you problems in the end. If not at least wrap them in electrical tape.
Other than that good to know cheers.

Fair call, thanks. When I was crimping them on I was thinking they were a bit dodgy. My soldering skill suck though, so I will try the taping first and see how I go.

So cheap, so simple.

Yeah, that's what I thought to. I am trying to figure out how the likes of Hayman Reece justify the cost of their towbar + electrics given how cheap and simple this solution is. I got my OEM (made by Best Bars in NZ) towbar off eBay for $400 odd, plus this electircs kit, plus $70 for the expert services of AlexG to help me fit the towbar up - so it was just over $500 all fitted up. Call it $600 at worst. *shrug*

[jimbomort]

well done arctra, always great to see someone taking the alternative route and finding a good solution

cheers

[z1000]

I have discovered the MY12 wiring is slightly different, there are only 3 wires into the light cluster rather than 4.

On the right, there is a black/green (indicator), black/purple (brake), brown (earth). While left has a black/white (indicator), yellow/green (brake?) and brown (earth). I wonder if brake and tail share the same wire now.

Can anyone with access to a wiring schematic or service manual confirm I have identified the correct wiring as per above?

[Umai Naa!!]

I'd say you're close to being on the money.

Stop/tail already shares one single filament globe. So why not share a wire on the output side? The Central Electrics module already steps the voltage up at the globe to differentiate between a tail light and a brake light. You do this using just one wire to the globe. The Central Electrics module already receives an input from the headlight switch, and one from the master cylinder travel sensor (AKA brake light switch).

[z1000]

Thanks Umai, is the central electrics model housed inside the light cluster?

Any idea how I can tap this single tail/brake line into a bypass relay to output tail and brake lines separately?

[Umai Naa!!]

Nope. Central Electrics module is above the fuse carrier under the right side of the dash.

I would tap into the feed from the headlight switch on the dash that goes to the Central Electrics module to get a tail light signal, and then do the same at the master cylinder travel sensor on the master cylinder for a brake light signal.

If you do it this way, you wont or shouldn't have any bulb monitoring issues.

For the trouble you'll go to to get it all working, you'll wish you got the genuine kit. Shoot me a PM if you decide to go down that path.

[z1000]

It looks like the bypass relay I got can take a single brake/tail input and output brake and tail lights separately. Give it a try I guess.