Yep, 12 volt + from an ignition source to one side of the temp switch.
My 6.2L cranks fast and starts good when it's cold, down to about 5 degrees. After that, the block heater is a must. It's also very vital that you have two strong, matched batteries, excellent battery cables, good grounds, and a fresh starter. This makes all the difference for a good starting 6.2L. My truck wasn't starting very well last winter, I had to leave it plugged in all the time. I put new batteries in last fall, and it starts so good now, I haven't plugged it in but a couple of times.
I actually made my own automatic glow controller out of a time delay relay and solenoid. It keeps the plugs on for about 15 seconds. I also have a momentary switch inside to over-ride the plugs manually on really cold days, plus to help with after glow when needed. There's another switch that shuts the auto function off during warm weather. I've found that during the summer, I only the glow plugs for the first start of the day. Unless it's sat longer than 8 hours, I don't need to glow to get it started. This helps save the glow plugs and puts less strain on the electrical system.
As far as glow time goes, it depends on what kind of glow plugs you have. The stock plugs are either 9G's or 11G's, but they burn out very easily if left on more than 10 seconds. The better kind are called 60G's, used in the later 6.5L diesels. They don't burn out nearly as often, and can be left on for longer periods of time. The best plugs are known as "quick-heats," and aren't supposed to burn out at all. You can get them from
www.kennedydiesel.com
Casey