Originally Posted by
alaxfire
Remove the negative battery cable and then connect a 12v light bulb between it and the terminal.
Use a backup light bulb or similar or a 12v test light.
Start pulling and reinserting fuses until you see the light go out.
Investigate from there.
Would a light ever go out with all the "normal" drains on the car?
A digital volt meter would probably be the way to go - just not sure how much of a spike you would need to see to determine you had found it..