Dear B.B.,

Hope you're well and stay so!

For the Crank Position Sensor / RPM Sensor (Volvo #3547847) - used in and after 1991 models - coil resistance is 170Ω ± 30. Source: Volvo, pocket data booklet - Cars 700,850, 900 (1991-1996), p. 40.

Sometimes transient conditions disrupt electrical systems. Thus, the SRS warning light may suddenly illuminate, for no obvious reason Disconnecting the negative battery cable clamp from the negative battery terminal - and waiting 10-20 minutes - usually re-sets the system.

At the risk of laboring the obvious - for which forgive me - auto electrics are subject to temperature and humidity changes: metal expands and shrinks. A coating of corrosion a few molecules thick - so invisible to the unaided eye - can disrupt a circuit. Corrosion increases resistance, sometimes to the point where power doesn't flow. But if the connector vibrates - e.g., when the engine is turned-on - the contacts may move just enough for current to find a path. The same is true as to heat.

Hope this helps.

Yours faithfully,

Spook