I've kept alot of my trucks 6 volts, being sure to use 2/0 guage, battery/welding cable. Most of the time, starting problems occur when, in the past, someone has installed modern, smaller cables(12v), in place of the larger(6v)cables.

Spanky Hardy
Collector Of Fine Old G.M. COE Trucks & Antique Holmes Wreckers

1948 Chevrolet 5700 COE Holmes HD W35 Wrecker
In the Stovebolt Gallery
More pictures on Photobucket

1950 GMC 250 1-Ton
In the Stovebolt Gallery