I agree with all the other info except this. The glow plug relay uses some funky internal electronics to measure proper glow time including an electrolytic capacitor which can change its value over time and even not being used for a long time(although that condition is temporary) The sensor you refer to as B is used by the climate control to delay application of higher blower fan speeds until the coolant temp is something like 52C. This prevents cold air being blown out of your heater on winter mornings until the coolant temp has risen somewhat.

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.