I personally have not had to do this but I found this online and it seems correct Disconnect the battery from the donor car, ensure polarity is correct, turn your ignition switch on, place the "hot" jumper lead on the starter motor side of the solenoid, the starter will spin without damaging the 6v system, DO NOT press the starter button.
I get all kinds of answers and I don't know which is the one I can count on. Every time I try to start mt old truck, it sounds like this is the time the battery is going to let me down.
I bought a motormaster jump starter and power bank 1200 A but don't know where to connect it on a 6 volt system without blowing something up.
Does anyone have the definitive way to jump start an old 6 volt safely ? Thank you