One way is to check the Delco Remy tags on the gen and starter for part numbers and then cross ref them at a friendly parts store. Often times the tag also said 12 Volt right on it and that would be even easier for you. All else fails run the starter off a 12 v battery and jumper cables. If it spins pretty quick it is 12 volts. If it spins like it wants to go into low orbit it is probably 6 volts.
If you can read any of the printing on the coil they usually say 6 volt or 12 volt, or "use with external resistor" which is a 12 volt coil.
Any idea what this engine might have come out of?
