As I recall that is the way the solenoid worked, it switched the batteries (two 6v batteries) between series and parallel.
Found some current info:
6 Volt Series Parallel Switch Relay 6 Volt DC To 12 volt DC 1500 amp Series Parallel Switch Used on Older Cars & Equipment Start On 12 Volts & Keep Your Original 6 Volt Charging System.
http://www.texasindustrialelectric.c...1119845_6V.asp