Mags are grounded to turn them off.
With the switch in the off position, both mag terminals should be showing ground. With the mag switch in Both, the terminals should be simply open, no connection to either ground or b+.
In the Left position, the right mag will be grounded, and vice versa.
The only thing that gets switched b+ is the starter, or starting vibrator if equipped.
There is a ground terminal that must be hooked up to chassis ground, so the internal connections will work to turn off the mags.

__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."