The only way these contacts get closed in when you pull the KEY out.
Like said above they are NOT designed to be left in this mode very long.
Each BRAKE MAGNET will draw 3 AMPS when 12VDC is applied...
If you have two axles then that is around 12AMPS of DC CURRENT for four wheel electric brakes.
ETRAILER.COM should a good replacement switch assembly for you...
I have heard on here of some users like to pull the KEY to use as a brake to hold the trailer in place. This really isn't a good idea as you can see what happens to the contacts and the BRAKE MAGNETS can also melt down which is probably on the expensive side.
Something like this google photo
Roy Ken