Need help finding new temperature gauge

I don't want to fry my gauges if they're still good - can I ground my set of resistors to the battery negative terminal as well? That little contraption is working quite well - I was proud of myself, even as bad as the soldering was - I got exactly 25 ohms.

I think the toughest thing will be to get 12v just to that one pin without hitting any of the other pins. I'll probably use a female spade connector and jam it over the pin so I don't risk a wayward alligator clip. :)