I would suspect the voltage stabilizer, the small component that supplies 10v to the temperature and fuel gauges. It is located on the back of the dash near the two major gauges. The stock ones use a bimetallic strip type deal. 10v output voltage cannot be reliably checked with a voltmeter as they are going off and on rapidly to supply an average 10v; the gauges are damped enough they don't move. You may be able to check the stabilizer output for ~12v to say ~13.5v to see if the devise has failed with the bimetallic strip in the electrically closed position.
Solid state replacements are available from Moss, or I believe John made some up a while ago.
I would just replace the thing and try things out as the component is pretty cheap & easy to get at and they are known to fail. The solid state units can be checked with your voltmeter for 10v output.
http://www.mossmotors.com/graphics/prod ... 31-555.pdfThe fuel gauge behavior sounds like it is being supplied with over 10v and the gauge reading is shifted up. Mine works correctly (sort of) in the critical lower range, but will never get to a proper full reading. Note the low fuel light should work correctly as it is a separate circuit from the tank sender. 12v supply to the two gauges would also account for your high coolant temp readings.
Once sure of the 10v supply to the two gauges, I still had to 'adjust' my temp gauge with additional resistors in series with the sender to get it to read correctly at various temperatures determined with candy thermometer in the coolant.
Note the oil pressure does not use 10v stabilized supply, rather it uses nominal 12v so should be different issue, although it sounds OK to me.
http://www.lotuselan.net/uploads/smiths ... wiring.jpgGood luck with the repair. HTH
Posted: Mon Jul 02, 2012 9:34 am
