You can also use a campers compass held up close to the brake magnets and you should see the needle deflect when the brake signals are applied.
Some brakes also make a tone noise when activated. Both my trailers do this... You have to be real close the wheels to hear it...
each brake magnet will draw around 3AMPS DC current if the full 12VDC is applied. So add your brake magnets and see if your DC current is close to that number for all brakes... Four brake magnets could draw as much as 12AMPS DC CURRENT when 12VDC is applied.
Roy Ken
