I installed an electronic heater valve that loops coolant in the engine compartment when closed, and then opens the loop to the passenger compartment when required. It is variable so you can control the heat. The under dash cable is hooked up to a potentiometer that is supplied. Got mine off of E-bay. Ask the guy if he will sell you the one minus the crimping tool. Needle nose pliers work just fine. You also have to extend the wires with some ribbon cable, and adapt the heater hose at the core if you want to eliminate the mechanical valve.
E-bay Pantera Heater Valve
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