In my '65 Imperial with a "Sentry Signal", the oil pressure and temperature each have separate sending units for the regular gauge and the "Check Gauges" light. The fuel system is limited to one sending unit, with the "Sentry Signal" tapping into the Fuel Gauge to warn when it reads below a certain point. Paul In a message dated 4/9/2004 12:10:41 AM Eastern Daylight Time, cbody67tx@xxxxxxxxxxxxx writes: > Whether the "sending unit" is running a gauge or an indicator lamp, it's >sending information in two different manners. A "sensor" uses varying voltage >to make the gauge needle more in the appropriate direction for the amount of >voltage it's sending through the circuit. A "switch" is either "on" or "off", >hence it is used for an indicator lamp that's either lit or dark (i.e., >temperature warning lamps, "cold"/"hot" light displays, oil pressure warning >lamp) > > In the case of the Imperials with the gauge AND indicator lamp, there should >be an oil pressure sensor and an oil pressure switch on the back of the block, >each with different circuits and functions, even if they might screw into a >common > fitting on the back of the block. > > Just some thoughts, > W Bell