The two 6 volt batteries are wired in series to provide 12 volts, like the old British cars such as the MGA do. Somebody probably swapped the ground sometime in the past, as almost all GMC's of that vintage left the factory as + ground. Move the E-brake to the back of the main transmission- - - -brackets should be available to do that or you can fabricate your own. Ed Pruss can probably provide some information on that brake system if you send him a PM.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!