This is the replacement defroster plenum I installed on my 1966 Mustang heater box. The plenum routes warm air from the heater box up to the defroster vents, and the original one on my car was cardboard.
The new plenum fits the 1965 and 1966 Mustang heater box and replaces the old cardboard part.
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Defroster Plenum at a Glance
- Replacement defroster plenum for 1965-1966 Mustangs
- Replaces the original cardboard plenum
- Has the internal piece already built in
- Hose clamps are not included
Why I Replaced Mine
After 50-plus years, a cardboard plenum isn’t doing much. Since I already had the heater box out for a full rebuild, it made sense to replace it.
One thing that confused me: I couldn’t figure out where a leftover piece from the old plenum went. It turns out the new plenum already has that piece built in, so you don’t need to transfer it.
Who This Plenum Is For
- Anyone with a worn or damaged cardboard defroster plenum
- Owners with weak airflow to the defroster vents
- Anyone rebuilding the heater box
How I Installed It
- Remove the old cardboard plenum.
- Fit the new plenum to the heater box. There is no need to move over the internal piece from the old one.
- Reinstall the heater box under the dash.
- Connect the defroster hoses. Order hose clamps ahead of time, since mine didn’t come with any.
See It in Action
I installed this plenum in my 1965-1966 Mustang Heater Box Rebuild. The post and video show the whole process.