Ok what i did to test the earth on the thermo switch is using a multi metre i hooked up the posotive lead to the postive on the battery and the negatve to the thermostat housing. I got a healthy reading of 12.14v, so the i hooked up the negative to the body of the thermo switch and got the same reading, so doesn't that mean the thermo switch is earthed??? There is a no hardending sealer on the thread.