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Thread: Tow bar electrics

  1. #1
    Join Date
    Jul 2005
    Location
    Barnsley, UK
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    46

    Default Tow bar electrics

    I'm fitting a tow bar with dual electrics onto my UK '89 525i saloon. I've got the bar on (loved drilling them holes!) and am about to cut the bumper in a sec, then it's on to the electrics.
    I've been given a guide on which colours to use for the main lights etc, but have a couple of questions:
    1) How do I get the wires into the car, from the towbar? Is there a nice entry point, or do I have to drill, if so, where do I drill to?
    2) Where do I wire the 12v wires for the battery & fridge on the Grey plug to? Am I going to have to take a new wire from the fuse box to the boot, or what?

    Any help appreciated asap as I'm doing it now! (I know, organised as ever!)


    Thanks

    Ben

  2. #2
    Join Date
    Mar 2006
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    811

    Default

    Need some more info on what you are doing. I have seen alot of tow bar installs where the tail lights are just tied into the trunk harness and then oyu close the trunk on the wires when you tow. I actualy like this method for infrequent use, since it keeps the connector nice and dry in the trunk when not in use.

    You sound like you are hauling a camper though. Does the camper have it own battery? you will need an isolator if you plan to keep it charged from the cars alternator. There are plugs under the carpet where wires can be pulled through for a permanant install of the BMW harness. Are you using a BMW towbar or an aftermarket one? BMW harnesss or aftermarket?

  3. #3
    Join Date
    Dec 2004
    Location
    Sydney, Australia
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    4,331

    Default

    BMW have a special relay box. If you don't use it, the warning diagnostocs will screw up. You need to add a relay to all the connections you use, so making your own realy box is a good idea if not using the factory one. It may not work like the factory one though, who knows. You might be able to source enough current (12V accessories and 12V constant feed) from the old phone wires if they are still running through the back seat beside the main loom.

    I ran my external connector wires without drillling a hole, it went in an existing grommet in the middle but I had to thread the wire up and down through the sandwiched rear panelling. Suggest you undercoat all your holes before you bolt through them. Factory uses hardened nuts and bolts for good reason too- with washers.

    Oh yea, and search the forum for Horsecock, much will be revealed...
    Last edited by genphreak; 06-01-2006 at 06:13 AM.

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  4. #4
    Join Date
    Jul 2005
    Location
    Barnsley, UK
    Posts
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    Default

    I'm towing a caravan, yes and it's an aftermarket kit.
    As I said, it'I've got the bar on, just sorting the electrics out. I don't know if it's the same stateside, but for in the UK we have 2 sockets on the towbar, one for the trailer lights (Black "N" socket), indicators, etc. and another one which can be used to charge the caravan battery and run the fridge (Grey "S" type.
    I don't have a plug in harness type thing, just a load of scotchlok connectors & instructions that say things like green on trailer wire (left flasher) connects to blue/green of car, blue (fog light) to yellow/black, etc. Which is fine for the trailer lights, but the instructions for the S type are a little les helpful.
    It has a relay & tells me to find a "suitable heavy dutyt +12v feed (either the + terminal of the battery, or a power feed to the fuse box)" and it's this I'm not sure how to find.
    I think I've found the way to get the cables into the car, I just need to work out how to remove the black plastic trim in the boot.

    Thanks for taking the time.

    Ben

  5. #5
    Join Date
    Jul 2005
    Location
    Barnsley, UK
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    just so you know, it's a fixed, flange type of towbar, I'm willing to take the risk with my shins for the price difference!

  6. #6
    Join Date
    Dec 2004
    Location
    Sydney, Australia
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    The trim comes off (but is brittle, beware), you have to pop the little rivets, centre comes out first- new ones are available if you screw them up at the stealer for pennies. Don't just suck the power off the car system raw. You need relays and you need a suitable feed, it is not like connecting wiring on a Morris. The BMW wires are all monitored by failure sensing systems and carefully designed fuses and relays for their exact jobs. You should want to understand the wiring you are tapping into or it will fail at the worst possible time. In UK that means, darkness, towing, driving rain and freezing cold... such a problem might take the rear lights on the car right out, or easily worse... Scotchlocks are a no-no if you ask me, they will ensure failiure. Sorry to mkae it sound so hard, but it is worth getting it right.

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  7. #7
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    Mar 2006
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    You can pull a wire from the battery to the trunk, there are gromets behind the rear seat back for passing the wires through. I would use a small battery cable, the same size as the alternator charging wire, I am not sure what the metric size is. You can either get a BMW strap fuse holder or get a suitable fuse from a stereo shop. Make sure that the camper battery is properly isolated, A simple relay can do it in theory if wired up properly, but I trust isolators more. I would be a bit nervouse about using any of the trunk harness wires to recharge the camper battery since it could potentialy need a large amount of recharging at times. Do you plan to go to camp grounds? this would make a difference in choosing how you handle charging the battery. Most of my experience here is from working on my fathers rigs, he would spend his summers living on dead end logging roads in the pacific northwest and would be totaly isolated from the world.

    BMW designed a tow hook for your car, I would follow their lead as much as possible when taping into the tail lights. That way you will have a nice clean install and every thing will work, it may not bother you to have the tail lights failure lights on now, but it will get on your nerves when you are on vacation and you don't want to worry about anything.

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