You can carefully jump a 6v system/battery with a 12v battery. Make sure the lights are switched off. As soon as the engine catches/starts, disconnect the 12v battery jumper cable,

I have done this safely/successfully a few times. I carry a 12v battery powered jumper /accessory system (and have had no problem using it).
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Last edited by Peggy M; 04/04/2024 8:36 PM. Reason: added image
Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.