Also watch
out for the middle lead of three-terminal (78xx/79xx)
voltage regulators...it's not unheard of to bring them up above
ground a bit with a voltage divider to make them operate at different
voltages.
The _middle_ lead is not ground on the 79xx parts!
The 'rule' I remember, at least for TO92 and TO220 packaged 78xx/79xx is
that the middle pin is the most -ve. Therefore it's common on the +ve
ones (78xx) and input o nthe -ve (79xx) series.
-tony