a crimping too is used to apply connectors to wire, they literaly compress the connector to the wire. If your wires are showing signs of heat, the heat is caused by the electrical energy (amps) passing through a loose connection .
You say you installed the circuit board, what did you do to the connectors that slip onto the tabs on the circuit board. Were these wires damaged?
Your last board was damaged by high amperage passing through the relay and the circuit traces. When your replaced it what else did you change?