What was found
CREW REPORTED AFTER TAKEOFF, RMU 1 DISPLAYED ALL DASHES EXCEPT COMM 1 WINDOW. RMU 2 DISPLAYED ALL DASHES. 115 VAC BUSS OFF ILLUMINATED FOR APPROX 30 SECONDS AND THEN EXTINGUISHED. DECLARED AN EMERGENCY AND RETURNED TO DEPARTURE. LANDED WITHOUT INCIDENT. ACFT REMOVED FROM SERVICE. R & R RMU 1, OPERATES OK IAW AMM 23-81-01. R & R RMU NR 2 OPERATES OK IAW AMM 23-81-01. REPLACED SWITCH FOR THE ACFT POWER ELECTRICAL SYS IAW AMM 20-13-04. OPS CHECKED GOOD IAW 24-20-00. ACFT RETURNED TO SERVICE.