I guess you have the original coil still in the car that has the base that bolts to the firewall?

Well, it was a crude early form of theft prevention. Most coils have a 12V+ terminal (that's switched on when the key is 'on' or 'cranking'), and the pulsed ground to the distributor points. If you got the hood open, it was easy to jumper a wire to the 12V side, then short the starter and get the car running. Volvo made this hard by having only one visible terminal on the coil, the one that leads to the dist. The 12V+ is hidden in the base, which actually fits through a hole in the firewall. And sticking with the theme of theft prevention, that connection is inside an armored cable that leads straight to the ignition switch.

Neat enough idea the the time I guess, a thief would have to supply their own coil to make off with the car. But it makes it a bit tougher to swap the coil these days.

Long story made short - you'll need to carefully cut the armored cable and tap into the 12V+ inside it and run that to the + side of the new coil. It's the only wire on the car (that I know of) that's hot only when the key is on, and also hot when cranking.
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'63 PV544 rat rod, '93 Classic #1141 245 +t