MSD installation
 

Most advice suggests the large red +ve MSD wire should be connected directly to the large +ve (from battery) starter motor cable, thus to a positive source that is live all the time, independent of the ignition switch. There is a similar constant positive power source at the small fuse panel under the plastic cover in tne left rear of the engine area which I plan to connect the large red MSD wire to, as it is near to the point where I am mounting the MSD unit. Does anyone think this is not a good idea?

I forgot, the car is a 1981 911 SC.

Power Source
 

The MSD unit will pull a couple of amps per 1000 rpm. Just make certain that the fuse will handle the load. I ran a lead off the main power lead on the starter for the MSD in my SC. It is easy to do and you can run it thru a piece of small diameter vacuum hose for extra protection. Just use some tie wraps to run the new lead along a protected route. Piece of cake!

same year as yours, my car is an 81. when i bought the car, the PO pulled power from one of the three fuses in the panel. i fried one. i rewired it to the starter lug, with a proper inline fuse. i feel better about it. running the wire is easy if you follow the AC lines down the right side. you can poke them thru super easy.

How can letting the My Spark Disappears unit run 24 hours a day be a good idea?

Nevermind I see the MSD has a switched input.

Thanks for all your comments. Will report back after installation.