You are now dealing with a clean 12v signal from the battery and it's telling you the battery is not charged enough for the system, thus it shuts off. You have got to get that charging system figured out before you deal with the EFI system. Watch you did not foul your plugs again holding it at 1500.

1968 Pro-Touring Dodge Charger
*2011 Optima Ultimate Street Car Challenge Invitee
http://www.popularhotrodding.com/features/1203phr_1968_dodge_charger/index.html