Heil furnace NUGK100DH08 runs continuously. Awakened this summer to the sound of blower running. NO central air. It has a shut off switch wired to it so I turned it off. I read that the transformer can cause this so I put my volt meter on it while it was running. One side of the voltmeter I touched to the connector where the yellow wire is attached and the other side of the voltmeter I stuck into the twist connector where the black wire is. I made sure that the probe was touching both ends securely. I pushed in the safety switch on the blower cover door and the motor came on. I got no voltage from the voltmeter. The thermostat was then turned up to call for heat and the furnace did light properly. Still no voltage from the transformer. Is this the proper way to test it?