Someone posted a link in another thread to the FSM. From that I was able to determine that it's either the blower regulator or the blower switch. Neither one is cheap, and ACC sucks even when it works right. Thanks to the data in the FSM, I was able to establish a pinout of the blower regulator 12 pin connector and wire in a toggle switch that allows me to have the blower on about the 4th or 5th speed. It works well enough to get me through the winter. Eventually if I find the motivation I want to switch it over to manual climate control.

Edit: Now I should probably start fixing the heater in the blue thing.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.