The Stovebolt Site Forums The Shop Area The Electrical Bay 6V and 12V at the same time?

I converted to 12V but want to run my 6V wiper motor and a 6V Press-a-Lite from a 12-6V converter.

Here is my question: both 6V devices are grounded to the body - so there is 6V going in from the converter, but where would it go back?
Over the body to the battery - but that's the 12V circuit, and than - wehre would the negative 6V lead of the converter go? Probably not on the body?

Am I overthinking this? I just don't want to ruin something.

thanks, Frank