Keeper: Defeating Headlight Warning

["Al Powell" <APOWELL@agcom.tamu.edu>]

Thanks to information supplied by the Hon. Igor Kessel, I came up 
with a low-tech way to defeat the headlight warning which is a 
nuisance when using a wiring harness to power european lights.  Note 
that this information applies to a 1990 200.  (Igor's car is the same 
model, one year different...)

Igor clued me in on finding the unit which provides the warning.  
That information is as follows:

> The unit in question is located in the auxillary relay panel, under 
> the dash.  Middle row, second from the right, looks like a standard 
> Hella relay. It is not. It's is a logic controller, P/N 443 919 
> 469B, built around a single chip. The chip listens to the current
> that flows through two very low reference resistors, comprised out 
> of two 15mm wires no less than 1mm in dia, probably Ag (they are 
> silver colour and have a very low resistance). The circuit listens 
> to the impedances of the low beams filaments and throws a red flag 
> (6v on terminal "K", goes to a thin grey wire, that is connected to 
> the kompooter) if either of two conditions are met:

> 1. At least one filament is blown (R=infinity) or
> 2. R of one filament significantly differs from R of another one. 

Igor made an elegant fix by using a non-functional relay which fit 
the hole, and by hardwiring it internally, then plugging it in.  
Pretty, but I didn't have such a spare relay body....

I did it the easy way by pulling the logic controller and making two 
short (3") jumper cables of 14-ga. wire, with a male spade bit (blue 
code) on each end.  I then inserted the spade bits into the relay 
connections to jumper both headlight circuits. 

NOTE:  You cannot defeat the warning just by pulling the logic 
controller and leaving it out of the circuit.  If you do this, the 
low beams **do not** come on - only the "city lights".  The high beams 
do work, however.

Igor's directions tell you where to jumper: 

>  For now I can suggest my non-destructive method. You want to shunt 
>  those calibrated reference wires. You need to connect 56bR to 56bR1 
>  and connect 56bL to 56bL1. 

This is VERY easy to do, as the pins on the logic controller are 
labeled exactly as Igor says.  Just pull the controller and CAREFULLY 
make a diagram of the contacts on the relay panel (which is a mirror 
image of the relay - so don't screw it up...) and you will know 
exactly which connections to jumper.  Double-check this before 
inserting the jumpers - it's easy to screw up!!

Hope this non-detructive method helps others turn off that #%&&*$ 
headlight warning.

Happy New Year!!



.......................................................
Al Powell, Ph.D.                 Voice:  409/845-2807
107 Reed McDonald Bldg.          Fax:    409/862-1202
College Station, TX 77843      
Http://agcomwww.tamu.edu/agcom/satellit/alpage.htm

"Some people can tell what time it is by looking at the
sun...but I have never been able to see the numbers."
             [From 5th/6th grade essays....]