electrical query - bench testing components

[toadster]

Hey guys - I'll admit I'm a bit novice when it comes to electrical - but learning...

I have the Wilwood Electric Parking Brake and I'd like to bench test to ensure it's working properly before I get into final mounting locations

I have the rear EPB calipers mounted with the clamping servos on the rear brakes and wired up, the switch is crimped to test, and I have a 12V benchtop battery for power (tested at 12.71v)
I've also tried the regular car battery (tested as well)

assumptions:
BATTERY (+) means connect to the (+) on the batter (duh)
GROUND (-) is (-) battery
ACC or IGNITION ON is specifically stated not to connect directly to the battery but a switched 12V

here's the Wilwood schematic


we put one of the 2-blade on/off switches in the circuit (like below) - but I'm not sure how to run the (-) line back to the battery, assuming the EPB takes care of this through it's own GND (-) line


without ACC connected we get 12V - but the unit will not power up (assuming the ACC is a momentary trigger)
with the ACC connected through the switch, we only get 3V (not enough to trigger IMHO)

any ideas? I'll reach out to Wilwood as well, but I thought maybe my learning can help others on here too!!