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BMW 3-Series (E90 E92) Forum > BMW E90/E92/E93 3-series General Forums > Regional Forums > UK > UK Technical Forum > e92 tow bar wiring.



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      09-02-2017, 02:09 PM   #1
Minisi
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e92 tow bar wiring.

Hi all,

have just installed a tow bar to my lci 335i, have wired up the relay module to the tow bar electric socket all i need to do now is wire the relay into the cars harness.
I have trawled through loads of google searches and posts on several forums, all of which are american and seem to have different coloured wires.

Any one here in the U.K. help me out with these couple of wires which are stopping me from getting my jet ski in the water😩.

thanks in advance.
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      09-03-2017, 07:07 AM   #2
AlwynMike
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Are you using the 7 way relay type or the Dedicated type?

7 way relay will need wires to the socket, then Scotchlock the sense wires to each of your car's rear lights - left and right rear lights separate, stop lights on one wire.
You may need an "anti-chatter" module on the brake light one, or connect the sense wire to the high level light (if you can find the wire!)

If you are using the Dedicated relay, the module will plug into the car directly, the wires for trailer lights go to the socket, and you often need a separate power wire. You will probably need to Scotchlock into the CANBUS wires too.
I can't remember what colours the CANBUS wires are, but the two will be twisted together (orange & brown???).
If you're using the Dedicated box, what make is it - you should be able to Google it and get some wiring instructions

Mike
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      09-03-2017, 10:12 AM   #3
Minisi
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Hi Mike,

thanks for your reply.

I have the 7 wire relay module that PF jones recommended i use.
I have wired the 7 pin socket to the relay but haven't connected the relay to the cars wiring as unsure on the colours i need to tap into using the scotch locks provided.

can't find any info anywhere that would tell me what colour wire does what on the loom? ☹️🤔
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      09-04-2017, 08:18 AM   #4
AlwynMike
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I'd just put a voltmeter on each terminal and see what voltage is on what when each light is on.

Pre-LED rear lights, BMW used to pulse the brake lights so they were acting as additional rear lights when the brake wasn't pressed. Not done an LED unit so can't comment on what's what with LED units. (I used the dedicated on mine)
It's a bit more difficult to find the high level brake light wire
Its easy enough to drop out a rear light unit to check the wiring.

You'll need to run a couple of wires across from the opposite light unit for that side rear light and indicator. These wires don't need to be very heavy as they carry next to no current - they just sense the light being on, the relay does the heavy work.

Mike
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      09-07-2017, 06:48 AM   #5
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Quote:
Originally Posted by AlwynMike View Post
I'd just put a voltmeter on each terminal and see what voltage is on what when each light is on.

Pre-LED rear lights, BMW used to pulse the brake lights so they were acting as additional rear lights when the brake wasn't pressed. Not done an LED unit so can't comment on what's what with LED units. (I used the dedicated on mine)
It's a bit more difficult to find the high level brake light wire
Its easy enough to drop out a rear light unit to check the wiring.

You'll need to run a couple of wires across from the opposite light unit for that side rear light and indicator. These wires don't need to be very heavy as they carry next to no current - they just sense the light being on, the relay does the heavy work.

Mike
really struggling to sort this out. tried a volt meter but to no avail, don't think the probes are thin enough to get to connections in plug.

Mike where did you get your dedicated harness from and how much was it? thinking a plug in and forget option would be much easier.
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      09-07-2017, 04:17 PM   #6
AlwynMike
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I got my kit from some obscure online company that I can't remember the name of.

I have used ECS in the past, and I think Right Connections too.

Looking at ECS, the kits are around 140, but I'm pretty sure that I paid just over 100, but that was 4 years ago. (I remember paying 150 for my 5 series kit 10 years ago - and I thought it was a bargain, as they were more than double that at the time).
Check out the ECS website as the instructions are available so you can see what's involved.

Mike
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