MEL LIFT DUMPER RESULT IN SECOND WARNING AND TKOF ABORT.

Narrative

OPERATING FLT FROM BUF TO PIT. WHILE WAITING AT THE GATE A MASTER WARNING CAME ON OUT OF THE BLUE INDICATING A RED MESSAGE; LIFT DUMPERS UNSAFE; ALONG WITH A 3 BELL ALERT. MAINT CHKED THE SYS AND COULD NOT RESET IT. OPTED TO MEL LIFT DUMPERS SINCE WX WAS VFR WITH NO RAIN AND RWYS WERE LONG AND DRY; WELL WITHIN REQUIRED SPECS FOR OPERATION WITHOUT LIFT DUMPERS. WHEN MAINT GOT SYS LABELED AS MEL; PROCEEDED WITH TAXI-OUT FOR TKOF. WHEN TAKING THE TURN ONTO THE RWY; WE PERFORMED THE FINAL CHK WITH THE FO CHKING VISUALLY THE LIFT DUMPERS AS BEING RETRACTED AND TESTING THE TKOF NORMAL REST BUTTON; WE RECEIVED A 3 LEVEL ALERT. BY RUNNING THE PWR LEVERS UP FOR A QUARTER THE ALERT DEFINITELY CAME ON AGAIN AND WE RETURNED TO THE GATE. THE SPD AT ABORT WAS NOT YET REGISTERED ON THE AIRSPD INDICATOR NOR WERE BRAKES USED OTHER THAN NORMAL; BUT WE WERE ON THE RWY ITSELF AND VACATED SAME. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ACFT EQUIPPED WITH 2 COMPUTERS VERSUS NORMAL 3. AS A RESULT MAINT MANUAL ARE NOT COMPLETE IN SO FAR AS WIRING DIAGRAMS ARE CONCERNED; HAD PROBS TRYING TO DE-ACTIVATE THE 'LIFT DUMPER' SYS. AFTER RETURN TO THE RAMP A MECH MORE FAMILIAR WITH THE ACFT WAS ABLE TO COMPLY WITH THE MEL AND THE ACFT WAS FLOWN TO PIT.