Hi mate
What I have done is run a wire to the pressure switch through a relay when the pressure drops it puts the pump on untill the accumulator on to of the pump is charged up again.
I tried to run the pump of the brake switch but when the pump keeps running it pushes the pedal up and makes the pedal hard.
I cant remember of hand which two pins I used on the pressure switch but can find out if you have not sorted it
Also you need the abs block or you will not be able to bleed the brakes it took me a week to find this out.
My brakes are now very light to push but very keen