E34 Service Indicator Light Reset
1. Turn Ignition off.
2. Short pins 7 + 19 with wire (remember to put a fuse on this wire).
3. Turn ignition on and wait for about 4 seconds for an Oil Service reset, 10 seconds for an Inspection reset, then
4. Remove the wire.
5. Replace the cap on the diagnostic socket.
6. Turn ignition off again.
You must do it exactly the way described above. Otherwise it won't work.
NOTE: These steps/instructions are what worked for ME. I do not promote them as something that's recommended to do. If you do try this you are doing so at your own risk. I'm in NO WAY responsible for damages cause in connections with these steps. They worked for me on my e34 many times!
Remove the cap from the diagnostic socket (right side of the engine bay on my LHD) and this is what you will find - well, my drawing of it anyway. The pins marked with red are the ones you are looking for. Use the cut in the center Mr. Pacman for pin identification.