Heat in a wire (or switch) is the result of more current passing through a circuit than the circuit is designed to handle. Excessive current draw in your simple circuit is likely caused by
a) faulty component, ie bad led or bad driver
b) faulty wiring, ie positive wire contacting ground at some point, either touching a wire or metal. LED + touching a grounded heat sink.
c) faulty design, ie you choose the incorrect driver, led combination