As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AT HIGH POWER SETTINGS THE RPM AND TEMPERATURE INDICATIONS WOULD BECOME INTERMITTENT. INVESTIGATION REVEALED THE EGT/CHT HARNESS ON THE RT BANK OF CYLINDERS WAS ROUTED TOO CLOSE TO THE EXHAUST SYSTEM AND WAS BURNING THROUGH THE INSULATION OF THE WIRES. CONNECTOR FOR THE TACH INDICATION WAS DISASSEMBLED, CLEANED, AND REASSEMBLED. OPS CHECK FOLLOWING THIS WAS OK.