Before you tweak fuse legs, be sure your ground connection is solid.

Here's a way to find out which leg is resistive or open:

Get a cigar lighter plug with the wires to alligator clips
Get some jumper cables or a heavy wire to the battery and a little
alligator clip for the headlight

Get a car headlight and clip a wire from the battery positive
and the cigar lighter ground to the headlight and see if it lights bright.

then clip the lead from the battery negative to the light and the
cigar lighter positive. It should light again

If you have a ratty "+12V" or "ground" this should tell you which side to
search. ie: If the headlamp doesn't work with the jumper on the positive,
then you have a crappy ground return circuit

Using a headlamp puts a load on the circuit that could possibly fool a
multimeter that doesn't draw doodelysquat for current.

Good luck... and post back, Bill