The Stovebolt Site Forums The Shop Area The Electrical Bay Voltmeter ticks down w/heater motor speeds

I`ve pulled the negative off the battery while the truck was running.
No change in the motor or headlight brightness. ALT is good?
Its having a hard time cranking,like the battery is low. I am trying to diagnosis
this so I don`t get stranded. Strange the voltmeter drops as I change heater motor speeds. Is that a sign
of something? The battery seems fine. 327sbc