850 fuel and temp gauge doesn't work

[misuli18]

Hello
My father has volvo 850 and odometer didn't work, he changed the gear and instrument panel worked 1 week as it should, then odometer stopped working again and he took that new gear and put it to another volvo 850 instrument panel. and he tested v70 instrument panels also, i dont know why.
Then fuel and temp and lights stopped working. Light fault was faulty light relay which probably didn't like v70 instrument panels.
But why fuel and coolant temp gauges won't work.
At a start both 850 instrument panels worked except odometers, and now neither of them works.

Is there some fuse or relay?

[WhatAmIDoing]

The odometer does not display, or the odometer and speedometer do not measure speed/distance? My fuel and temp gauges read wonky, and I still have not been able to figure out why.

[misuli18]

odometer works now but fuel and temp gauges won't

[scot850]

Have you tried pulling another speedo unit and fitting it to see if the circuit board has failed? Did both of those items work before and stop working at the same time? If they were bad before it may not be the speedo, but could be the sender units themselves (the ECT temp sensor for the temp gauge, check the connector at the power steering pump, and check the resistance values to make sure it is reading correctly), and it could be a bad earth or fuel level sensor in the fuel pump or in the wiring, particularly at the fuel pump itself.

Neil.