One trick I've used to replace wiring through the frame, you might find handy - is to find both ends of the wire.
I cut the end closest to the Coil/Regular/Alternator/whatever that damn thing is.
Tie the end of the new wire to the end of the old wire....then slowly pull the old wire through the frame till the new wire comes through, and then pull off and chuck the old wire.
Connect the new wire to your splice (I use auto connectors for this), then go back and cut the OTHER end, and splice that.
That's if the wiring itself is bad, tho.
Did you try using a Voltage tester on it for continuity<sp>? , cause that can tell if you it's just the wire, most of the time.