[ngoma]

Temp sensor at the front of the cylinder head is for the temp gauge.

Temp sensor at the rear of the cylinder head is for the glow plug relay.

Solenoid near the base of the IP is the altitude compensation timing advance. Connects to a rectangular microswitch screwed into a barometric diaphragm (shaped like a slightly undersize tuna can-- look for it in your parts boxes)(On the Volvo it was mounted on a bracket on the inner fender next to the GP relay). Important that that solenoid gets +12VDC under normal run conditions, otherwise the engine will run a chronic overly advanced timing condition. IOW, that solenoid should be seeing +12VDC at altitudes <4,000 ft. My opinion: That subsystem was designed backwards. A better design would have been a mechanism requiring no voltage at normal conditions, energizing voltage for high altitude.