I drove around for about a year without a working alternator by paralleling a tractor battery to the standard bat & charging with a 25A charger when I got to mains power. Now trying to fix. The Valeo alt brush cap was full of dust so i thought the reg had shorted so bought a new reg assembly from the UK fitted but still no good. 0.5V on the small terminal and 12.5V on the big one regardless of running or stopped. Altern will excite if fed 12V on one of the brushes & neg to chassis. Seems like a computer problem. Any suggestions?