I do not drive the Caprice in winter so I have not really paid any attention to it.
The FSM says the first time you tap the switch you get 10 minutes. After that 5 minutes.
The FSM does not give the amp draw for the defroster but several people have reported it "wore out" the 30 amp breaker.
Using just math:
I do not think GM would put a 30 amp breaker on a 1 Amp circuit and I doubt 12.5 Watts will heat a back window.
I expect the defroster to draw 15-25 Amps which would be 0.8-0.5 Ohms.
Most meters are not accurate under 1 Ohm.
When you set your meter to Ohms touch the probes together. If the meter does not show zero subtract that number from what you measure on the grid.
From the math I expect the grid should be under 1 Ohm
Another way to check would be to measure the current draw. Not many people have a meter with a 30 Amp range.
For testing only:
If you replace the breaker with a 30 Amp fuse (and it does not blow) the math says the two contacts on the top of the fuse will have [email protected]
Amps or [email protected]
Amps. 30-50miliVolts requires a good Volt meter.