B737 First Officer notices slightly different electrical panel during preflight and queries maintenance. Maintenance replied that the newer panel was being installed in the older B737's and is acceptable. During taxi out the decision ias reversed and the crew instructed to return to the gate.

Narrative

During preflight; I noticed the AC/DC metering panel on the cockpit overhead panel was slightly different than I'd seen normally installed in our 737's. I looked in the aircraft flight manual and found that the panel in question is installed on the newer aircraft in our fleet; so I conferred with the Captain. He called our Maintenance and Engineering department and explained the situation. During their conversation; It was determined that the new panel is currently installed on our newer models in the fleet and would be installed on the older models as well; so we could legally depart. After we had departed the gate; it was discovered by our Maintenance and Engineering department that the new panel had not been approved for use in the older aircraft at this time. During taxi-out we received an ACARS message telling us not to takeoff and return to the gate. After an unsuccessful search for a replacement panel; the flight was cancelled. It is my belief that a contributing factor in this situation is a manager's decision to cut costs by removing the older panels from inventory leaving only the newer ones available.