Which wire is generally switched, hot or ground?

[MEdwards]

Thanks, Jan. Great first post! Very interesting. I never thought much about it, but now that you mention it, my electrical engineering education in the late '60s was just as you said. The first time I encountered "electrons and holes," different currents flowing both ways, was when we first studied semiconductors my junior year. As I recall, it didn't clarify much!

Of course all this interesting academic stuff is auxiliary to the OP's original question, which also is the title of the thread. He never mentioned +/-, he asked about hot/ground. That question was answered within the first hour, in the second message.

[Al Burgemeister]

As I recall some Fords also had a positive ground, i.e., the positive terminal was tied to the frame. Until those vehicles were no longer around some accessories had to be made to work either way. The norm now is to switch the positive side and to ground the negative side to the frame.

Al B12

[FlyingRon]

In my experience you can find switches both on the ground side or the ungrounded side in aviation and automative applications.
In the case of the Navion, there's one place where there's both. The gear horn circuit goes like this:

+ BUS --- breaker (share with starter) --- throttle switch --- horn --- gear_down_locked switches --- frame


If the throttle switch indicates the throttle is below a certain MP setting and the gear is not down the horn sounds. I found this out because the guy who installed my XM Radio had three active high and three active low inputs to mute the audio that he could connect things to. However neither side of the horn itself will provide a signal that is active high or low with it sounding. If hooked to one side it mutes the radio (or not) with the throttle position and on the other side with the gear being down. It took me a while to figure out why the radio only played when the gear was down.