If you are doing like the you-tube video and are using a 1 ohm 10 watt resistor then what you are seeing is 37.8 mili volts or .0378 volts. Using the formular I=E/R or amps = voltage/ohms. Then amps = .0378 or 37.8 mili-amps. That seems like a normal reading for a 420.
My 84 500SEL will go dead if not started for 3 or 4 weeks and it reads about .03 milamp if I remember correctly.

Paul

__________________
84 500 SEL (307,xxx miles)