brakes

Please i'm at a lose, i've tried everything i can and i'm thinking of putting in a 93 mustang sn95 booster and master cylinder,i really would prefer to leave everything as close to stock as i can, but i'm getting quite frustrated.

The gy/y wire goes to the ignition switch thru the blue fuse link and is the power for the relay coil. The other side of the relay coil is grounded thru the PK/LB wire going to the pressure switch. The motor will not run if the pressure switch is not working because the relay coil will not be grounded and the relay will not connect power to the motor. What you have done is bypass the relay thru the ignition switch. You already have determined that there is no continuity between terminals 1 and 4 of the pressure switch and that is why the relay will not switch. If you jumper 1 and 4 in the connector at the pressure switch with the ignition on the pump should run if everything else checked out as you indicated above. I can't find any connector in my book where GY/Y changes to W/R that has anything to do with the brake system, but the GR/Y from the blue fuse link to the splice also goes to the oxygen sensor, the EEC module and the ABS module from the splice so its important to the operation of the engine as well as the brakes. If you didn't have power to operate the relay coil before and you do now after splicing in another wire to bypass that section of the GY/Y, that section of the wire must have been faulty. Try a jumper between 1 and 4 at the pressure switch connector to see if the pump motor runs.