No NS switch on column shift manual trans cars. Besides it would only affect starting; your symptom package has the circuit opening with a load. It would not be in the circuit after starting. I think a visual inspection of the ignition switch is called for. The back part is crimped into the pot metal front. If it is loose it should be replaced. Based upon a list of $59 for ign switch # 116 462 00 93 you can probably get one for 30-40 bucks.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician