I'm a newbie in the 911 world and have an '83 911SC. I popped the hood and realized that this blower motor was not connected to anything. There was a piece of duct that came from the main engine fan that was easy enough to reconnect to it. However the wiring wasn't plugged into anything and it was just kind of in place without any fixturing/fastening into place. What is this motor used for?

 

That motor supplies heat to the cabin from the exhaust heat exchangers. The red levers between the seats turns the motor on. Seems like someone disconnected it, probably because the motor is shot and making noise.

 

yeah that motor doesnt last long .
it was added in "later" cars as it was found early cars without it did not have the ability to clear the windshield of condensation and ice at low RPMs and idle, as the engine fan doesnt run fast enough ( likely a safety update, mandated or otherwise ) . beyond idle it does nothing as the engine fan vastly overpowers it and takes over. Many people " backdate " the heating systems and remove this fan altogether and route directly from the engine shroud to the exchangers. Lots of info on the net about this modification.

if you take it apart for fun you will likely see the board that the brushes mount to, completely burned out..