Slick Magneto FAQ

How do I check for a "hot" magneto?

Continental Service Bulletin SB653 (or latest edition) contains information for checking to see if the magneto is "hot".

SB653 in Acorbat format

In addition, the following is provided by Hartzell Propeller

Mag Check
Periodically ensuring that your magneto’s p-leads have not broken is a good defense against unexpected starts on the ground. These leads, which are connected to the ignition (or magneto) switch in the cockpit, are responsible for grounding the mags to keep the engine from running. Sometimes the wires or connections between the switch and the magnetos break or come adrift. In this case, one or both mags may be "hot," or ready to deliver spark whenever the prop is turned. To test them, instead of shutting down the engine in the usual manner with the mixture control, use the key. Allow the engine to cool normally and idle down. Move the key slowly through both Right, Left, and then to the Off position. The engine rpm should drop slightly at both of the individual-mag positions and shut down completely in the Off detent. Allow the prop to stop and then move the mixture to the idle-cutoff position. Do not try to "catch" the engine before it comes to a stop because a dangerous backfire might occur. If the engine does not stop when the key is in the Off position, shut it down with the mixture, prominently mark the prop as being "hot," and contact maintenance personnel immediately.

There are a few other caveats to consider when in the vicinity of the prop.

Avoid pulling the airplane around by the prop. Yes, this seems the perfect solution to a vexing problem of how to change the airplane’s position without having to walk around and get the tow bar, but it’s worthwhile to make the extra effort. Neither the engine nor the prop particularly benefit from the loads imposed by horsing the whole airplane around.
Avoid pushing the airplane by the spinner. The spinner and backing plate are built to be light, so they’re quite fragile. Pushing on them can cause the backing plate to crack and can lead to spinner failure.
Avoid contact with prop deice boots and associated wiring. If you want your hot prop to be toasty when it counts, stay clear of the boots.