Like Carter said, it's 3.45vdc per cell. Vehicles run a 12 volt system but are actually 13.8 volts in most cases.
3 neutrals will create steam, not HHO. The only chance to get this to work properly is to reconfigure it like Carter said, but with such a small surface area (12.5 sq.in.), it's not going to produce much (maybe 0.3 LPM) at the maximum amp. draw of 6.25.