Trailer hitch for Audi, and trailer wiring

[Mike Arman <armanmik@n-jcenter.com>]

Avi Meron sez:
>
>To all our esteemed q listers,
>Da Lang Mfg. have trailer hitches for Audi,
>The phone # is: 508.425.9585
>Da Lang also have a trailer wiring set-up (taps power from the battery) via
>relays,

Spoke to Da'Lan this AM, got a FAX from them with wiring diagram of their
adaptor for Audi - cost $51.00 or so - unless there are relays inside that
box, it is wrong and will trip the bulb-out warning light in the autocheck
system.


Have a Da'Lan hitch on the car (86 5KS), went right on - fits well, can't
get the tongue to come out of the receiver - rusted in, tried Kroil, heat,
BFH (Big *** hammer), so I'll leave it in place . . 

Then Tony K in Toronto sez:

>*** There are a few different kinds of three bulb to two bulb wiring 
>conversion kits available.  The cheapest are only about $20.  The $60 
>versions guarantee your vehicle electronics from frying, and are not 
>supposed to confuse the "bulb-burnt-out" car circuitry.  Can anyone shed 
>some light on this?  Which should be purchased for late model Audi's?  ***


Problem is that Audi's wiring a) has the bulb-out autocheck, and b) is, as
we all know _JUST_ adequate for the existing bulbs.

Preliminary solution will involve a trailer light "combiner" from Discount
Auto Parts ($12.00), and some wiring into terminal 54 on the bulb-out sender
in the trunk (terminal 54 is brake lights), and a relay plus new hot wire.

Wires are: Combiner Red (brake lights) to terminal 54 on MCU ("monitor
control unit")
           Combiner Brown (parking lights) looks like it could go to the
license plate light wire (or luggage compartment light, hot side, as source
of 12 volts-when-lights-are-on) - BUT these wires will be undersized for the
extra load, so there will need to be a relay connected to the lic. plate
wire which will control the relay, and connects the Combiner's brown wire to
a hot wire - probably from the battery, which Audi considerately placed
close by, under the rear seat. Don't try to cheat this and eliminate the
relay by just replacing fuse S14 (or S4) with a bigger 20 Amp fuse -
something else will burn out first!
            Combiner yellow to left turn sig bulb
            Combiner green to right turn sig bulb
            Combiner white to chassis ground.

Terminal 54 on the MCU is "upstream" of the sensor, so extra loads tied in
here won't upset the sensor - what the MCU tells you is that your BRAKE or
TAIL light bulbs are out - has nothing to do with the turn sigs. 

Note: The relay will have to have a duty cycle of 100% - whenever the lights
are on, the relay will be energized, trailer connected or not.

I'm going to wire this in probably this weekend, so if you are not brave and
would prefer to see if MY car can pass the "smoke test" instead of yours,
you'll have to wait for next Monday for results. Otherwise, this SHOULD
work, and costs less than Da'Lan's part, which I am not sure is correct anyway.

Probably a good idea to buy an aftermarket fuse block and fuse all the
wires, too! (Don't fuse the white - ground - wire) About 5 to 7 amps each
should do it . . .

Best Regards,

Mike Arman