The HVAC blower motor will not turn on. We tested the motor by applying 12v directly to it and it works fine. We then installed a new blower motor control regulator to no avail. Finally we installed a replacement dash unit but that also had no effect. The dash unit lights up all the buttons work fine. We ran the diagnostic function on the dash unit but there were no errors. We're stumped as to where to look next.

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2000 Mercedes S500
1990 Mercedes 560SEL
1970 Triumph Spitfire