We have been trying to get our truck to acuratly rear on the oil pressure guage and water temp gauge. With mechanical gauge and temp gun the oil pressure should be well into the normal range not hanging to the low side with 40 psi hot idle. After changing out other senders the problem stil is there. The temp gun says 185 at the t-state but guage read close to cold. Again changed sending units and reading are the same. I did a quick test of ICVR by putting test light on temp wire and it light up and down when motor was running. Could old gauges be bad or is there something else we are missing. Thanks Al

 

I think it is the ICVR. I've never done the test you mention but it seems the light would light even though ICVR may be bad, After all, your gauges are movin a bit. Not dead.

 

Why didn't you test those two gauges ?

Just touch the your two sender wires to ground for a short time gauge if good should go all the way up to high or hot.
Orich