I don't have that model, but IMO the voltage would be 0 (or close to 0) or 12 V
DEPENDING on how the controller is set up.
Most smart controllers will not apply the brake voltage unless their was forward momentum.
So to apply the brake sitting still might not give you any reading.
But if you have the gain and sensitivity set high you might see 12v or what ever the source voltage is. Might also hit 12 V then trail off to close to 0 V.
1984-2014, 1984 21' Hi-Lo Fun Chaser, 1972 C-20
2001-2013, 1995 34' Airstream Excella, 2001 F250
2013- Now, 2006 Itasca Meridian 36G, Jeep GC