Thanks for the reply. In the past, I have checked a sensor ground, that according to the wiring diagram, went to the automotive computor. I used an led with a resistor, came off the positive battery post, touched the ground wire, and this was a constant ground, the lite came on, so I guess the ground was ok. I just wondered about using the logic probe.
I wondered if the probe put out any voltage, I checked it with a volt meter, couldn't find any. With the probe leads grounded, the lower case lite came on. The lite came on because both leads were grounded completing the circuit for the lite? thanks