Connected a light pen from to neg cable to neg post to observe when light would go out when fuses were taken out.

Discovered the removal of 9 would make the light go out, but ..

only when C and 9 we both out at the same time.

If 9 was taken out, but C was left in, the light would stay on.

9 controls the diagnostic module, among many other functions.
(Started with Check engine light - on after key out!)

Noticed the transmission selector lever position light is not working - controlled by 9 also!

What does this mean and what should I do next?

__________________
1991 300E 124.030 103.983KE 722358 03 412178
207K

1979 240D 123.123 250K (Project car)

2000 Ford Ranger, 187K

2015 Dodge Ram 1500 EcoDiesel 37K