AN MD82 FLC CHANGED TO TWR FREQ; PREMATURELY; WHILE HOLDING SHORT OF THE RUN-UP PAD. THE ATCT TWR CTLR INTERVENED AND RELAYED THE GND CTLR'S INSTRUCTIONS.

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AFTER GATE DEP GND CTL TOLD US TO CONTINUE ON TXWY RB BUT HOLD SHORT OF THE RUN-UP PAD AT RWY 4L. WE DID. GND WAS VERY BUSY. NOT UNUSUAL FOR AN ARPT THE SIZE OF EWR. THERE IS; OR WAS; A LARGE WHITE SIGN IN OUR 1-2 O'CLOCK POS THAT SAID TO SWITCH TO TOP ANTENNA FOR TWR (PROBABLY FOR BETTER RADIO RECEPTION); SO WE SWITCHED TO TWR. AS WE ALREADY USE TOP ANTENNA FOR GND OPS; WE USED #1 RADIO; WHICH HAPPENS TO COME OFF OF THE BATTERY BUS. A FEW MINS LATER; TWR JUMPS ALL OVER US FOR BEING ON THEIR FREQ AND HE INFORMS US THAT GND SAYS TO FOLLOW THE SECOND ACFT ON THE L. AT VIRTUALLY ALL VERY BUSY MAJOR ARPTS; RADIO FREQ CHANGES ARE DONE AUTOMATICALLY AND UNFORTUNATELY WITHOUT ACKNOWLEDGEMENT. IF AN ARPT WANTS SPECIFIC PROCS TO BE FOLLOWED THEN THOSE SHOULD BE EMPHASIZED AND WRITTEN DOWN. WE DO TRY TO HELP OUT BY NOT 'TRASHING THE RADIOS' WITH USELESS SPEECH. SUPPLEMENTAL INFO FROM ACN 330650: WE COULD HAVE PREVENTED THIS BY CONFIRMING FREQ CHANGE WITH GND. AT OUR HOME BASE (ORD) WHEN GND IS VERY BUSY WE CHANGE TO TWR WITHOUT CONTACT.