Mark Houlahan
Brand Manager, Mustang Monthly
December 15, 2013

For those who drive their vintage Mustangs in the fall and winter months, having a functioning heat and defrost system is essential for driver safety and comfort. If it's 40 degrees outside, just keeping the windows up and the cowl vents closed isn't going to warm the interior. Once you start driving, the cold air hitting the windshield is going to create visibility issues that a functioning defrost system can remedy (versus a quick swipe with a towel at the red light—you know who you are).

Rebuilding your heater system to fully functioning status is a rather easy job that just takes a few basic hand tools and a whole lot of muscle to get things cleaned up and ready to reassemble. The vintage Mustang's heater from '65-'68 featured a fiberglass box with two manually adjustable divider doors, a heater core assembly, and a bolt-on cardboard defroster/floor heat duct. The heater system is controlled by a set of Bowden cables and a basic electrical circuit that controls a blower motor to move the air through the heater system. General heater system issues include a leaking heater core, inoperative blower motor, and deteriorated internal seals that allow air leakage and reduce the system's effectiveness. We've also seen restricted airflow/heat due to leaves/twigs/nests built up inside the case.

Most everything related to the '65-'68 Mustang heater assembly is reproduced these days—even the heater box itself—save for a few minor parts when you get into the '67-'68 model years. National Parts Depot stocks everything you need to get your heater back into shape, including mechanical, electrical, and cosmetic parts. Let's tackle a typical rebuild so you can see just how easy and rewarding this project can be.

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23. New Bowden cables are the last piece of our heater rebuild puzzle. If you have sticking heater control levers or a lever that doesn’t move the control lever on the case, a new set of cables will solve the problem. Use the metal clamp on the heater assembly to adjust the cable’s throw versus lever movement to maximize door movement within the case.