Your on the right track Tom, These sensors are German remember. That means black is the signal wire and grey is the signal ground. So obviously it should have infinite resistance to the case from the black wire. The two white wires are the heater.
=========================================================== David Cooley N5XMT Internet: N5XMT@xxxxxxxxxxxxx Packet: N5XMT@KQ4LO.#INT.NC.USA.NA T.A.P.R. Member #7068 We are Borg... Prepare to be assimilated! ===========================================================