Hey TM First thing is all you guys make my brain hurt. LOL (not that hard to do) Your measuring voltage drop across the input leg of the circut, need to measure voltage after the 33ohm resistor. If Im right take your volt meter hooked from the pos batt terminal to the other side of the resistor. This will give you "X", subtract that from your potential voltage, should give you input voltage (boy I hope Im right). This way we should be able to measure input voltage regardless of what were using as a supply. I dont have a setup atm to prove it but thought you could give it try to see if it works out.
Growing old is mandatory, Growing up......optional. He is wise who gains wisdom from another's mishaps. —Plutius Syrus