For temp sender, voltage stabilizer and gauge testing and replacement in the early 240s, refer to pp. 53-60 in TP11402 Electrical Systems and Instruments Repairs and Maintenenace 1976-

A copy can be found here in the Oz Volvo technical archive
https://ozvolvo.org/archive/?download=Vm9sdm8vMjQwIEdyZWVuIEJvb2tzLzNfMzEtMzYsIDM4IFRQMTE0MDItMl9lbGVjdHJpY2FsX3N5c3RlbS5wZGY=

You'll need to source a test resistor of the specified ohms and tolerance or accurately set an appropriate pot, maybe adjust the gauge horizontal with it and re-measure the pot. The test resistor specified says to 1976, but will be the same as yours. All VDO clusters to 1980 apparently used the same voltage stabilizer, not used in the Yasaki's.

My own thoughts:

You've pretty much confirmed the voltage stabilizer has issues what with corrosion. Look at the pic in the manual to see how low the temp needle goes when off.

Are you sure your fuel gauge is reading normally? The gauge may peg high before the tank is actually full if the stabilizer is wonky, so maybe fill up slowly with the gauge on and pause occasionally to watch its progress. Generally, just above the 9 o'clock half full mark should be pretty close to half the tank capacity spec if you tippy-top up.

At warm idle, do the gauges move significantly when the headlights and blower on high are switched on/off? ->Stabilizer unless your alternator regulator and/or battery are shot


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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now