Jeff;

If I understand your explanation correctly, I'd say your method is at fault...a Voltmeter is used to measure voltage, and not pass current...by placing it is series with the load..."running the other terminal through my multimeter (set to DC) to the positive terminal" ...remember, a currentmeter must pass all the loadcurrent, so be in series, a voltmeter sniffs the voltage...typically you connect its neg lead to ground/chassis, and then sniff around for voltage with the positive probe. That's why you always refer to a voltage reading as: ...voltage across....

Suggested reading: http://www.intelab.com/swem/an_automotive_electrical_primer.htm

Cheers