I was an English motorcycle guy (think Lucus electrics) before I
started playing with MBs. One of the coolest tools i made was a fuse
tester. I took a 5 amp breaker (about $5 at Napa) and attached two
clips. I could put it across a fuse holder and it would complete the
curcuit without taking out the wirering if there was a dead short. I
actaully made it for finding dead shorts since the breaker would blow,
i would disconnect parts of the circuit until it stopped blowing.
However, for any electrical gemlins, the first thing i do is toss this
across a fuse holder and see if a fuse is bad. If everything works as
it should, then the fuse is bad. Something I do on my MBs, is if one
fuse corrodes, then I change them all out. I have a jar of spares int
he trunk. Quite handy.