Once you get the hang of using two shifters, a Brownie gives you a lot of options. Each main box gear will have three ratios to choose from, under/direct/over and the top gear overdrive position will give you a better top end speed. I'm planning to do exactly that with a 1961 American LaFrance pumper I've got stashed away out in the pasture, with a 401 GMC V6 and a driveline mounted fire pump. I got my Brownie in a horsetrade with another bolter down in Louisiana, so all I'll need to do is acquire some shift linkage. I'm also planning to discard the fire bed and install a commercial 5th. wheel and a gooseneck trailer hitch. Presently, the truck has a Clark 5 speed, but 5th. gear is direct drive, not OD.
Back to the original question about voltage and polarity- - - - -As much as I like to tinker with old-school DC generators and regulators, a 12 volt negative ground internally-regulated alternator somewhere in the 100-120 amp range will handle any reasonable electrical demand you're likely to encounter, including running the fire apparatus equipment in a parade, etc. One big 12V battery like a Group 30 should be all that's required, battery-wise. A General Motors 12-SI alternator from a big Oldsmobile or Cadillac from the 1990's should fill the bill nicely, and all that's really needed to swap ground polarity is to reverse the primary wires at the coil and swap battery cable connections, obviously. Everything else- - - -starter, heater blower, lights, etc. should operate OK on either polarity. The gas gauge might require a little tinkering to read correctly on a negative ground system. Good luck!
Jerry
