first would be to test the starter trigger wire itself, then trace backwards, to take out NSS from equation, its best to jump the wiring (beware the starter will now work in all ranges)

MB also have a security lockdown that cuts the circuit if the system detects something and they DO go bad.

__________________
2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)