Towbar Wiring

[camera doctor 25]

I am looking at fitting a towbar to the touring for summer, to tow the pop-top

Last year I towed it with the 540i sedan, but noticed that I got bulb errors on the display, due to the trailer wiring. It was wired by the previous owner, and was just tapped into the rear lights etc.

I understand that BMW do make a special module to isolate the trailer wiring, but I guess it its $$$$ ??

I have done some research on the US and UK forums, and have come across this system :

Modulite

Has anybody had experience with this or the BMW unit?

I notice the turn and stop output seems to be tied - is this only for USA cars that flash the stop lights for turn signal?

Any auto sparkies on here who would care to comment ?

TIA,

Greg

Edited August 16, 2010 by camera doctor

[39KiwiTouring 2]

Interesting you say it causes errors (pop top that is). I have had 3 caravans over the last few years including a pop top that caused me all sorts of grief effected my headlights, park ligts only, blew bulbs, left my break lights at rear on at night that lit up the pop top etc.

Spent about $1k at an auto sparky to be told that it is affecting my towing vehicle - umm yeah o.k.

Changed caravans and the problem went away, check the trailer wiring first mate thats where the grief will be.

I know the guy who bought my liteweight expander wripped it all out and started again with the traler wiring, not earthed, bad connections, rusted pins, list went on.

[camera doctor 25]

Interesting you say it causes errors (pop top that is). I have had 3 caravans over the last few years including a pop top that caused me all sorts of grief effected my headlights, park ligts only, blew bulbs, left my break lights at rear on at night that lit up the pop top etc.

Spent about $1k at an auto sparky to be told that it is affecting my towing vehicle - umm yeah o.k.

Changed caravans and the problem went away, check the trailer wiring first mate thats where the grief will be.

I know the guy who bought my liteweight expander wripped it all out and started again with the traler wiring, not earthed, bad connections, rusted pins, list went on.

Cheers - so you are saying your is just spliced direct to taillights, no special 'box of tricks' ??

[39KiwiTouring 2]

The one I have now has never been a problem plugs into the back of the E39 easy as everything works. I usually tow with my van though and this is what the pop top caused all the problems too.

Try some other cars if possible and see if everything works including the dipswitch break lights etc. Take the plug apart and clean it out and make sure all the wires are coatia as they get squashed etc, being what they are.

[elmarco 56]

No idea about that particular product, but I have heard the factory module is around $500 ish (unless you can get one on Trademe). I had BMWorkshop do mine in the E46 with relays, and I think it was around $200 installed (I was too lazy to do it myself). The car will be looking for a specific current draw (or resistance) during its self monitoring - so wiring directly into the rear lamp circuit will throw an error (more bulbs than it is looking for). Jochen/Glenn/Hotwire will no doubt be able to tell you exactly how it works.

I have also heard that the factory unit puts the car in trailer mode (holds gears longer etc) and switches off the parking sensors etc. Don't know how true this is though.

[39KiwiTouring 2]

It puts my E39 in trailer mode pain in the arse stays in 4th at 3500rpm at 100k, unless you use the steptronic to change manually it stays in lower gears but still pulls like you know what.

I tow with the van now as sitting at 3-5000rpm in the car is tedious.

[kwhelan 241]

I am looking at fitting a towbar to the touring for summer, to tow the pop-top

Last year I towed it with the 540i sedan, but noticed that I got bulb errors on the display, due to the trailer wiring. It was wired by the previous owner, and was just tapped into the rear lights etc.

I understand that BMW do make a special module to isolate the trailer wiring, but I guess it its $$$$ ??

I have done some research on the US and UK forums, and have come across this system :

Modulite

Has anybody had experience with this or the BMW unit?

I notice the turn and stop output seems to be tied - is this only for USA cars that flash the stop lights for turn signal?

Any auto sparkies on here who would care to comment ?

it would work by just tapping into the wires,preferably with relays and you just need to disable the bulb warnings with navcoder,this would be the cheapest option and wouldnt cause it to default to towing mode in the auto

i don't think the missing bulb warnings are that much of a loss

[hotwire 352]

it would work by just tapping into the wires,preferably with relays and you just need to disable the bulb warnings with navcoder,this would be the cheapest option and wouldnt cause it to default to towing mode in the auto

i don't think the missing bulb warnings are that much of a loss

As mentioned above & earlier in the thread - you can do with relays & run a separate power source for the relays. Doing this will not activate fault codes so those circuits won't need disabling.

DONT connect straight to lamp circuits - the LKM is not designed for this extra load

There are various aftermarket modules available in NZ for this situation - auto sparkys have access to these, & cheaper (but simpler) than the BMW option

[jochen 4]

Another option is keep your eye on TradeMe.

I picked up an original BMW Trailer Module Control Unit for my E39, complete with wiring loom, for $60

Dirt cheap, and made my car complete :-)

Otherwise, a handful of relays is the way to go... they won't impact on the load as seen by the LCM

[camera doctor 25]

As mentioned above & earlier in the thread - you can do with relays & run a separate power source for the relays. Doing this will not activate fault codes so those circuits won't need disabling.

DONT connect straight to lamp circuits - the LKM is not designed for this extra load

Thanks for that Grant, I'll grab some relays and wire thru those, should be the cheapest option !

Any commercial kit is just gonna be some relays in a plastic box anyway I guess !!

[red89mx 0]

I picked up a Modulite unit the other year for the E46, and even though i specified the euro model found it was a wire short of a good time.....forgot to think through how the Yank trailers were wired.

Can use it but need to add an additional relay for one of the sets of lights.

Just use the towbar for a bike (very occasionally) now and leave trailer duties to the 4WD. Must look to get arround to finding the unit again in my garage. Recon a set of relays will do the same job and be cheaper.

[letsparty.co.nz 0]

Just brought a E34 525i se recently it already had a towbar fitted but no wiring WTF!

Having read about the wiring issues, I understand why it was not wired up.

I salvaged 4x relays out of an old Nissan: LH Turn, RH Turn, Tail, Stop lights. one side of all relay coils were common-ed to earth, the other side of each coil was connected to the +ve wire for each light.

I then connected one side of each relay to a suitable 12v wire, the other side of the relay went fused to the appropriate wire on the trailer plug.

Works Perfectly with no issues, relay/fuse box fits neatly out of sight in the little recess below the tail light assembly.

Of course bulb monitoring for trailer does not work, nor does the towing mod. signals to auto transmission,

but no worries drives great.