What was found
(CAN) CREW REPORTED TRANSPONDER NR 1 & NR 2 WAS TRANSMITTING INCORRECT ALTITUDES. THESE ERRORS STOPPED FOR A SHORT TIME AFTER TURNING TRANSPONDER OFF THEN ON AGAIN. ERROR READINGS SUCH AS: INDICATED 7600, TRANSMITTING 10000 INDICATED 8400, TRANSMITTING 9600 AFTER INSPECTION MAINTENANCE FOUND CHAFED WIRING ON BACK OF THE CO-PILOT`S ALTIMETER "B1" SHORTED TO GROUND. WIRES WERE REPAIRED IAW WDM 129-340037 SHEET NR 2. PITOT/STATIC CHECK CARRIED OUT AND BOTH TRANSPONDERS TESTED SERVICEABLE. ACFT WAS RETURNED TO SERVICE.