I have to rotate my trailer wheel an half turn when jacked up to activate the electric brake magnet PADS on my trailer.
Some brake magnets produce a tone when activated. Some folks will hold their camping compass up close to the wheel and it will deflect when brakes are activated.
If you have a clamp on Sears AMPMETER you should read 3amps DC CURRENT on each brake lead when electric brakes are applied.
Also my newer 2010 F150 Truck that has built-in OEM brake controller will not send braking voltage to the trailer using the brake pedal unless the truck is moving down the road at least 10MPH. The slider manual switch is only way to lock up my electric brakes when sitting still.
Roy Ken