I have reset the 4matic code(pin 5,3 flashes,brake light switch)on my 1992 300te several times over the years but I can't find a solution to this problem in the threads.
My home made code reader led stays red always.Whether I short the ground,or disconnect it completely led is on.No difference if key is on or off.

Removed and checked brake light switch with ohmmeter,working properly.

led goes out when module disconnected.

4matic dash light is illuminated.

I tried other pins and reader works fine.

When I disconnect the battery,led stays lit for 2 seconds before going out.

Any ideas.