The P-mag requires a manifold pressure connection in order to control its timing advance. I had previously located a tee fitting in a convenient location, but I never finished it since I didn't have the right fittings on hand. Time to check that off the list, so here's a combination of fittings that allows me to tap off the 1/4" OD plastic hose with a 1/8" ID rubber line to the P-mag:
Here it is mounted on its little bracket. Note the pair of adel clamps on the left side of the image – they will become relevant later.
Manifold pressure line connected to the P-mag. I used the stuff that came with the P-mag, but it seems like it might just be regular old vacuum hose from the auto store.
Since I was working with the P-mag, I plugged in the power supply and verified that it gets power when the master switch is on (note green LED). I also set the crankshaft to TDC and blew in the tube to set the initial ignition timing, although I will probably adjust it again before I try to start the engine.
At some point while I was messing around in this area of the firewall, I started thinking, "hmm, there sure are a lot of things running through this area, wouldn't it suck if it turned out to be impossible to install and remove the battery now?" So I dug the battery out of the basement and tried a test fit. It's really tight with all that stuff in there! I had to push the ignition wires, ground strap, and oil pressure hose out of the way…
Almost there… it's like getting a battery-sized square peg through a series of triangular and oblong holes…
Home free now! From here it just drops straight down into its tray. Of course then I had to reverse directions and remove the battery again, which was equally painful.
Here's that manifold pressure plumbing again. I had to remove the adel clamps in order to be able to flex the oil pressure hose out of the way of the battery. Subsequently I decided to just leave them off – if these two lines turn out to rub together, I'll fix it with a dab of RTV.
Kids, do yourself a favor and think about battery replacement when you're locating stuff on the firewall. I didn't give it enough forethought and I almost screwed myself. Lesson learned.