I am assuming I shouldn't do it but I thought I would ask anyway. Nothing will be turned on. What about the generator and regulator, will they cook themselves?
Raf

This is how I have done this Raf. Not strickly a good thing to do but here goes.

Connect the jump leads to the 12 volt. Connect the negetive 12 v to the neg 6v
Turn the ignition on and crank the engine. When its cranking slowly on the 6 volt only connect the 12 volt positive to the positive 6 volt battery terminal.

Disconnect when the motor starts or when you stop cranking the motor.

The cranking starter will draw all the voltage away from the things that could blow up with too much voltage.

Disconnect the generator if you are worried about it.

fine, I do it on a fairly frequent basis.
give the old bluey a 12v kick in the pants.
connect the jumpers up to the 12v, and the -ve to the 6v. turn the ign. on in the 6v and get it turning, then connect the +ve as its turning. she'll start spinning a whole lot quicker than normal and won't take long to run. disconnect the jumpers fairly quickly as they start to warm up fairly rapidly.
heres a snap of ol' bluey

Hi

Do it the way suggested, but there is a risk of explosion from gases in the batteries, connect the - last to somewhere on the chassis or block on the donor car, that way any sparks are away from the battery.

1302Steve

sounds like a two man or woman job... and a bit iffy... I wouldn't do it....
In the old days when battery cells were connected together with large lead straps it was easy to get 6 or 8v from a 12 volt battery then... but its very easy to do damage to Your Coil voltage regulator & Generator plus everything else that is 6V and switched on....
Foot on the brake.... bulbs blown...
Radio On... Yikes...
Blinker or trafficators accidently turned on.. where's that smoke coming from???
Too dangerous for Me guys... Lee

from the previous post.... - means the negative terminal of the battery or earth on that vehicle...... it is a minus sign... not a mistake or I hit the wrong key.... LOL

The 12v battery I was going to use is fairly dodgy so it have about 9v only anyway. Should be OK, right?

Ive been doing it for years... no problems just once it starts up remove the 12V ASAP.

^^^^ As Dave said. ^^^^^

what Dave said, never blown even a bulb.

what Dean and Dave said.... I cranked my beetle till i saw some smoke coming off the (-) lead from the jumper leads from all the current being drawn... If jumping from your dodgy 12V batt doesn't start the engine, use on thats in a car with the engine idling... other wise you'll run the risk of having two flat batteries... just idling is fine,,, don't rev...

this is what i did...:thumb