CanBus and tow bar wiring. Technical

Jim Jamieson · 26th February 2018, 20:53

Here’s one for the technical minded.

Last week I fitted my tow bar and 13 pin electrics to my Mercedes CLS which has CanBus wiring.
The wiring kit (Westfalia) was extremely simple to fit as the 12 wires were pre wired to the socket and inside the car all I had to connect were two CanBus wires, the earth wires and the extra wires for the fridge and battery charging which again simply plugged into the fuse box.
There were no wires to connect to any lights as the control box via CanBus signals control all lighting on the caravan.

Now my question is could such a system be used on the 75.

I will soon be transferring the towbar from my current 75 onto my project 75 but would be quite willing to leave all the wiring in place if a CanBus system could be used.
On my current 75 I used an old loom to source the correct wiring colours to splice into the car loom. These wires were then terminated at a junction box along with the 13 pin cabling from the socket.

steve-45 · 27th February 2018, 21:05

I read some where that a "plug in" wiring harness was at one time available for the 75, but there a bit like rocking horse droppings now ...

(But I did manage to find an OE spec plug in harness for my 45)

Jim Jamieson · 28th February 2018, 08:00

I’ve never seen the OE wiring harness for the 75 but my Jaguar XF had a dedicated wiring harness where you unplugged the tail light assembly and plugged in the harness between the light and original loom.

The harness for the CLS had a significantly less number of wires, one of the reasons cars now use the CanBus system to reduce weight.

cb750chris · 28th February 2018, 17:43

Hi Jim,
Sorry to inform you, if you are fitting a towbar to the 75 it is a case of splicing in to the individual wires for the rear lights. I would recommend using a bypass relay (but some don't). This is the case even when using the genuine factory kit

The Mercedes sounds like the rear lights have a can bus processor within it to decode the canbus, whereas our cars have a bunch of wires from the light switch, the "only" feature used with the CAN bus is for bulb failure warning when used with the genuine towing relay box.

Jim Jamieson · 28th February 2018, 22:26

I suspected that the 75’s CanBus system would be limited in comparison with Mercedes, after they’re almost 2 decades apart.

I fitted the tow bar originally onto our diesel 75 then when I changed it over to my V6 I made up a loom from the wiring from a scrap 75. It’s a much neater installation than it was originally which was supplied with scotchlock type connectors and yes it does have the by pass relay.

26th February 2018, 20:53	#1
Jim Jamieson This is my second home Rover less ! Join Date: Jun 2011 Location: Tarbolton Posts: 3,442 Thanks: 393 Thanked 888 Times in 542 Posts	CanBus and tow bar wiring. Technical Here’s one for the technical minded. Last week I fitted my tow bar and 13 pin electrics to my Mercedes CLS which has CanBus wiring. The wiring kit (Westfalia) was extremely simple to fit as the 12 wires were pre wired to the socket and inside the car all I had to connect were two CanBus wires, the earth wires and the extra wires for the fridge and battery charging which again simply plugged into the fuse box. There were no wires to connect to any lights as the control box via CanBus signals control all lighting on the caravan. Now my question is could such a system be used on the 75. I will soon be transferring the towbar from my current 75 onto my project 75 but would be quite willing to leave all the wiring in place if a CanBus system could be used. On my current 75 I used an old loom to source the correct wiring colours to splice into the car loom. These wires were then terminated at a junction box along with the 13 pin cabling from the socket.

28th February 2018, 17:43	#4
cb750chris Trader Rover 75 Tourer Join Date: Apr 2011 Location: Portsmouth Posts: 849 Thanks: 201 Thanked 292 Times in 200 Posts	Hi Jim, Sorry to inform you, if you are fitting a towbar to the 75 it is a case of splicing in to the individual wires for the rear lights. I would recommend using a bypass relay (but some don't). This is the case even when using the genuine factory kit The Mercedes sounds like the rear lights have a can bus processor within it to decode the canbus, whereas our cars have a bunch of wires from the light switch, the "only" feature used with the CAN bus is for bulb failure warning when used with the genuine towing relay box. __________________ Now offering T4 services in the Fareham area Replacement keys programmed / supplied / cut Diesel 135 upgrade available IPK virginisation and T4 matching available Sorry, due to a big change in home circumstances, I am unable to do any large jobs at present, but can still offer evening time diagnostics.

27th February 2018, 21:05	#2
steve-45 This is my second home Rover 75 Saloon CDTi Join Date: Oct 2015 Location: Belvedere Posts: 4,076 Thanks: 108 Thanked 1,089 Times in 774 Posts	I read some where that a "plug in" wiring harness was at one time available for the 75, but there a bit like rocking horse droppings now ... (But I did manage to find an OE spec plug in harness for my 45)

28th February 2018, 08:00	#3
Jim Jamieson This is my second home Rover less ! Join Date: Jun 2011 Location: Tarbolton Posts: 3,442 Thanks: 393 Thanked 888 Times in 542 Posts	I’ve never seen the OE wiring harness for the 75 but my Jaguar XF had a dedicated wiring harness where you unplugged the tail light assembly and plugged in the harness between the light and original loom. The harness for the CLS had a significantly less number of wires, one of the reasons cars now use the CanBus system to reduce weight.

28th February 2018, 22:26	#5
Jim Jamieson This is my second home Rover less ! Join Date: Jun 2011 Location: Tarbolton Posts: 3,442 Thanks: 393 Thanked 888 Times in 542 Posts	I suspected that the 75’s CanBus system would be limited in comparison with Mercedes, after they’re almost 2 decades apart. I fitted the tow bar originally onto our diesel 75 then when I changed it over to my V6 I made up a loom from the wiring from a scrap 75. It’s a much neater installation than it was originally which was supplied with scotchlock type connectors and yes it does have the by pass relay.