Hi Brian

I am a bit suspicious that your problems are the result of the voltage stabilizer being faulty. Both instruments run at a little less than the usual 12 volts (9 volts seems to ring a bell). If both temperature gauge and petrol gauge are reading higher than you would expect, check the voltage on the supply wire, ie not the lead to the sender, if the voltage is 12 volts the stabilizer will be the problem. These units are usually trouble free but can give rise to problems if not correctly earthed. This is simple to do on the donor vehicle as the unit is mounted to the metal bodywork, on our cars simply mounting the unit to the fibreglass will not provide the necessary earthing so a seperate lead is required to bond the casing of the unit to earth. This is far easier than delving into the petrol tank electrics only to find that all is well.

Happy NGing
Mike