What was found
(CAN) SHORTLY AFTER GEAR DOWN SELECTED ON FINAL, PUFF OF SMOKE NOTICED BY PASSENGER IN AREA OF LT NR 1 & 2 WINDOWS. LDG CARRIED OUT NORMLLY AS NO FURTHER SMOKE. AS PRECAUTION A/C STOPPED & SHUTDOWN AT THE 1ST AVAILABLE RWY TURNOFF & PASSENGER UNLOADED. FAULT COULD NOT BE DUPLICATED DURING SUBSEQUENT GROUND TESTING SO AREPL A/C SENT FOR PASSENGERS FOR RETURN FLT, ALONG WITH AME TO INVESTIGAGE PROBLEM. THE AME FOUND THAT THEREADING LIGHT MOUNTED IN LT NR 1 WINDOW SERVICE PANEL INCORRECTLY WIRED, HAVING GROUND WIRE (#3A18) ATTACHED TO INSULATED POSITIVE POST OF LIGHT & 24 VDC WIRE (#L31A18) ATTACHED TO NEGATIVE POST, WHICH IS NOT ISOLATED FROM LIGHT ASSY CASE. THERE