|More info from Andreas Pretzsch : I've
got a BMW 525i (E34) from 05/1988.
There seems to be a LKM-B (basic) and a LKM-L (luxury).
LKM is the german abbreviation for "Licht Kontroll
Modul", the light control modul.
The same LKM, at least according to the part number, is in
the 750i from 1988.
LKM part number (on top of the case):
61.35-1 379 372
5 KG 005 175-00
According to the IC manufacturing date (1987 and 1988),
I assume it's the original part. Anyway it's a single board,
not the one on your pictures. Therefore the construction changed
Failure was the same, one relay solder point was cracked.
To be on the same side, I resoldered all points. Now it works
like a charm.
LKMs can be found at ebay easily for below 50$, sometimes
Functional details of the LKM-B:
In standby (low beams off), there are 9.8V at the fuse.
If you remove the fuse or the bulb, the on-board computer
The 9.8V looks like some kind of current limiting circuit
(current not checked).
When the light is switched on, there are 12V at the fuse and
of course at the bulb.
In case the relay (or the soldering point) is defective, there
are 0V at the fuse and no (!) warning from the on-board computer.