[V8] Remoting the Headlamp Sensor Module for Headlight Relay Upgrades

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Wed Nov 9 20:03:16 EST 2005

... this is one of those projects I'd like to document fully ... some

Basically you are half way there by jumpering the module in the fuse
block ... unfortunately that's the way it has to be since you are
powering the headlights from under the hood.  What you do is to install
the module you pull out of the fuse box in the relay panel.  There are
two circuits for the low beam lights ... wire them up just like they are
from the wiring diagram ... wait, I've got the wiring diagram here, let
me get some pin numbers.  The only odd thing that you will need to do is
to run a single sense wire back to the fuse box and plug it into the
location in the socket where the sense wire would connect.  I've
actually been able to snake a Teflon insulated small gauge wire back
through the harness ... no BTDT for the headlight sensor specifically
yet ... 

The module in question is labeled J123 and is called "Lamp Control Unit,
Front" and is located in position 7 in one of the aux relay panels.  The
module works by measuring a difference in the voltage drop across two
low value resistors, which means the current for the bulb has to pass
through the module on the way to the lamp.  The pin labeled 4/56L is the
supply for the left headlamp bulb, and the associated lamp is connected
to pin 8/58BL2.  The supply for the right headlamp comes in on pin 6/56R
and the bulb attached to pin 2/56BR1.  Pin 7/31 is to be attached to
ground.  The last pin on the module is pin 9/K.  This is the wire you
need to route back to the relay panel ... although it looks like you
could also intercept at a Kostal connector (T14i/4).  I would simply
crimp the appropriate male spade lug to the end of the wire fed back and
plug it into the relay panel where the pin (9/K) would have been
attached were the module plugged in.  Of course you will need jumpers
from pin 4/56L to 8/56BL2 and 6/56R to 2/56BR1 to supply the signal
needed to enable the relays with the headlight switch.  A preferred
situation might be to find a similar module and use the base as a plug.

Steve B
San Jose, CA (USA)
> Could you describe this process?   On my cars with relayed harnesses,
> used the jumper-replaces-relay "fix" that does not leave you with the
> sensor function.
> At 12:50 AM 11/9/2005 -0800, urq wrote:
> >... for all the hassle you have to go to for installing the Euros, it
> >really that much more difficult to relocate the warning module to the
> >headlight relay box and retain the functionality of the sensor ...

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