Quick update, had been rainy and today a nice day to be outside to follow up:


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.

EDIT: 9 controls the diagnostic module, among many other functions.
Noticed the transmission selector lever position light is not working!


What does this mean?

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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