Is this what it looks like?



Here is some info on a SPDT(single pole, double throw) switch which is what it sounds like you're describing.

http://www.kpsec.freeuk.com/componen...h.htm#standard

 

this is the exact switch I am using:

http://www.hella.com/produktion/Hell...LED_Rocker.jsp

 

The 12 volt goes to the middle prong and then you run a wire from the lighted terminal side to whatever you're powering. The ground on whatever you're powering is then hooked up to a vehicle ground. The "off" terminal on that switch is not used.

You could use the "off" terminal as a "on" terminal also like to switch power between two different devices. It's all said in that link I posted above.

Read the "ON-ON Single Pole, Double Throw = SPDT" section and look at the diagram on the side.

 

The switch could also be used to switch the ground instead of the power wire.