2001 Lincoln Town Car SUSPENSION PROBLEMS

HERE IS MY PROBLEM. I HAVE A 2001 TOWNCAR THAT HAD REAR END DAMAGE. THE BODY SHOP REPAIRED THE DAMAGE AND INSTALLED A NEW DIFERENTIAL IN IT BUT NOW THE SUSPENSION ISN'T WORKING. I CHECKED THE RELAYS, FUSES, HIEGHT SENSOR, AND CAN UP WITH NOTHING. THE ONLY OTHER THING I NOTICED IS THE CONNECTION TO THE COMPRESSOR HAS FOUR PINS AND ONLY ONE HAS POWER( ABOUT 5 VOLTS) EVEN WITH THE KEY TURNED AND THE CONNECTION TO THE HIEGHT SENSOR ALSO HAS FOUR PINS AND THREE HAVE POWER TO THEM ( ABOUT 5 VOLTS A PEICE) WITH AND WITHOUT THE KEY TURNED. THE SUSPENSION WAS FINE BEFORE IT GOT TO THE BODY SHOP BUT NOW IS AS I DESCRIBED IT. ALL I CAN COME UP WITH IS THAT THERE IS A SHORT TO VOLTAGE. AM I OVERLOOKING SOMETHING, OR HAVE I DONE ALL AND NOW NEED TO FIND THE SHORT?