[kirkf]

If I understand you correctly, you want to boost a vehicle with a 6 volt positive system, with 12 volts to get it to start. I assume this is so you can take advantage of the faster starter speeds.

Here is how I would do this:

1. Disconnect the lead from the starter to the starter solenoid at the starter solenoid.
2. Connect the 12V vehicle Positive to the 6V vehicle Positive
3. Temporarily clamp the negative booster cable to the starter cable to rotate the engine. Unclamp it once the motor starts.

-You don't want to allow 12 volt power to reach the rest of your vehicle, because not all components are rated for 12 volts. (Instrument cluster is an example)

-Don't run the starter for too long like this.

-Remember you need to unclamp the negative booster cable as soon as the motor starts.
(The terrible noise you hear will be a hint)




Kirk