Keep in mind..
A voltmeter is not always the best tool, troubleshooting 12v systems..
They are sometimes too sensitive for the task..
I have been fooled more than once, by a digital voltmeter..
It will sometimes read 12-13 volt, but there will not be enough amp's to light a 5W light bulb at the socket...
Most Car electricians, uses the oldschool circuit tester with a built in bulb..
For circuit testing i mean..
It is a little different, when testing circuitboards..
I always have one of these lying around... : PICO WIRING 0690PT - Pico Circuit Testers - Overview - SummitRacing.com
Just my thoughts tho...