[Cartman]

youll see 12 volts across the terminals reguardless of the switch position due tot he fact that your tester will be completing the circuit, not the switch. the only true way to test the switch is a continuity test. if you must test for voltage, then you place the neg(-) side of your DVOM on your neg(-) batt terminal, and the pos(+) side of your DVOM to the ground terminal of the switch. when the switch is engaged, you will have a 12v signal coming from it.
As a side note, NEVER use a test light when diagnosing new vehicles. damage tot he computer will result! ECUs dont use full 12V as signals, and most signals are extremely low amperages. using test lights may inadvertantly send full batt voltage tot he ECU and fry it. Not to mention if you accidentally get into an airbag harness.....BANG!