if you're rheostat/light switch has fritzed out you can PROBABLY just
cut it out of the circuit by finding the 'light ' wire and connecting it to
a 12V source somewhere.  Your dash lights will be on full brightness but
they look nice that way anyway. Saves cost of new light switch!! :-)

Caveat: If lights look 'really bright' out some resistance in the 
power lead until they look okay.

with regards to finding correct wire I would go with bentley.

Stephen P. Smith
Director, Facility for Laser Spectroscopy
Department of Chemistry
Cornell University
Ithaca NY 14853
607-255-0580
607-255-4137 (fax)