What was found
CABIN EMERGENCY LIGHTS CHECK FAILS SYSTEM TEST. TEST GIVES FAULT EPSU EXT LOAD FWD L. INSTALLED NEW EPSU & BATTERY (10WL), NO HELP. REINSTALLED OLD EPSU & BATTERY. STARTED T-SHOOTING IAW TSM. RED LED EXTERIOR LIGHTS FAULT IS ON AT EPSU 10W L. NEED TO REMOVE LT OVERWING EXIT SLIDE FOR FURTHER TROUBLESHOOTING. PRIOR TO SLIDE REPLACEMENT RE-CHECK OVER WING EXTERIOR LIGHT TO INSURE OPERATIONAL AS THIS WILL ALSO CAUSE FAILED TEST. THROUGH TROUBLESHOOTING FOUND DOOR 1L SLIDE FAILING. REPLACED SLIDE. EMERGENCY LIGHT TEST NORMAL.