I want to install a volt meter in one of my Magnums, now, if I wire it at or from the (+) and (-) posts, will it run down the battery? Or, is there a better way to wire one up simply?

You want a switched 12v source or it will always draw on the battery.

Usually switched. Could plug it into the accessory terminal on the fuse box if it has one.
The load a voltmeter puts on a battery is very, very small. Hold for a few weeks? Sure. A few months? Don't know.
The one in my 72 SSP is taped from the ammeter gauge so it is hot all the time but the longest it has gone without driving is about two weeks.

This car's going to be a semi-daily driver, so setting long periods is highly unlikely. Wasn't sure where I could draw juice from so as to not run battery down.

Thanks.

I plugged one into my cig lighter.

So did I. I think I paid $12 at a parts store. Innova 7421.
R.

Got a digital one also. Works fine and was cheap.