Brakes don't "work"

Sounds like one of the two sections "might" still has air in it. Thats why the shuttle in the switch shoots over to one side setting off the brake light. Pumping the brakes will compress the air and build-up pedal. The switch will then return to its normal center position.

In your first post you didn't mention how you adjusted the rear brakes. The E-brake can be used to adjust the rear brakes, if its working properly. Get someone to apply it several times to see if you can hear clicking in the drums. Thats the adjusters ticking over. If it doesn't do that, then there is someone no working right in the back brakes.

If the adjustment is way off, you will also need to pump the brakes rapidly to get pedal. The MC may not have enough capacity in one stroke to push the shoes out to the drum. This could also be contributing to your problem. Thats way I think it might still be air, but this could also be your problem.

Another test you can do is to remove the switch from the switch unit (don't remove piping) and check which way the shuttle is moving. Its hard to see, but you can use the back end of a small drill bit to feel which direction the shuttle goes when someone pushes the pedal down. It will push the bit towards the front or back and then upwards 1 or 2mm. The direction front or back is what your trying to determine. The direction it moves towards is the section causing the balance issue. That will narrow it down to front or back.

Goodluck and keep at it, you will get there.

Chas