[lineslinger]

rbray,
Without being able to see how your system is configured I think it would be ill advised of me to offer a formula as to how it should be wired up.
USUALLY there is a lead coming off either the alternator or the battery or both which can/might/should be designated for a low voltage indicator light or a charging/voltage meter mounted on the dash.
Do you have a schematic drawing of your cars electrical system or maybe the gauge has some decent instructions?
Different systems use different routing for the indicators/gauge. Some will run a separate lead from the alternator to the gauge, others will run from the hot lead of the battery to the gauge while others will have the gauge wired in line between the battery and alternator.
See if you can't search the EM guys on this site and maybe someone will offer up their wiring schematics.
Sorry I couldn't help more, but misinformation from my end could result in melted insulation or worse on your end.
Good Luck.