The LKM is a module that often breaks on E34s. When headlights
suddenly quit working, or other erratic headlight behavior, the
LKM is often at fault. The LKM is the big "cassette"
located in the relay/module box in the engine compartment. It
may take a good yank to pull it out.
Note: The LKM in the photo's are from a Euro E34 (4 relays;
low beam, high beam front fog, rear fog) whereas most US LKMs
will only have 3 (no rear Fogs)
I know there is a procedure on bmwe34.net...
but I thought I would add some pictures so that people can see
exactly what fails and how easy it is to fix. As you know symtoms
include low beams that turn off on their own and other sporadic
Once you have removed the LKM module from the car you have to
extract the circuit board by carefully prying the edge of the
case apart and sliding the connector / board assembly out.
Prying the case apart
Other side, notice relays on both ends
Board out, relays down
Bad connections outlined in yellow
If you look closely at the above photo you will see that the relay
solder connections have fractured and are not really soldered
in any more. What you have to do is reheat them with a decent
soldering iron and add a little more electronics grade silver
solder. You need to add more solder as the flux in the new solder
will help re-establish the connection so your LKM will work again.
You can be anal and remove all the old solder and re-solder each
connection but it's not really required. (I don't like solder
Look closely at the relays and be sure to touch up all the contacts
(on both ends of the LKM)
If you haven't ever soldered before then Google it. Its not hard
Hope this helps some of you
Article by Byron Topp