Good news David, it appears you're making progress!
If I understand correctly you have 12 volt power, positive and negative, to the wheels but no brake action on either wheel?
Again, I'm not familiar with the electrical
system on your trailer but if you have ground to the hub (axle) and apply live (positive) to the coils, you have bypassed all the components of your braking system except the coils which you are now testing.
Do I understand correctly that the brakes don't work on either wheel?
These coils do fail but not usually both at the same time.