On arrival notice main fuse to power supply blown. Relocated power supply for UV light off of thermostat wires and straight to transformer. Once power to the air handler unit was initiated and a heating was energized. It popped the 5 inch fuse for power. Once fuse popped disconnected UV light from system. Turned on breaker unit thin pops another fuse. After some time I Was able to trace it down to the thermostat itself. I removed the power wire off at service connections in the unit. Thin generated power to the unit no fuse was tripped.. Pulled the face plate of the thermostat off the wall, visually inspected and noticed battery acid on battery terminals. Thin began to test the thermostat connection and received continuity between four of the prongs on the back of the thermostat that I used to call for heating cooling and fan thus being the reason fuses blown in the attic as voltage reading across all when there’s no call for heating / cooling. The face plate of the thermostat is remo