Hey all. Thanks for the replies and the information. My glow plugs all work and jumping power to them at the firewall-mounted coil for 8-10 seconds allows for an easy engine start. My research appears to show the power comes off the headlamp switch then goes to the plunger switch, the salt shaker and then to the glow plugs themselves. I assume the break is at the headlamp switch - seems others have experienced that in the past as well.

I've seen the pencil type glow plug videos online and while I'm not going to change mine out yet I am going to take the suggestion they make re upgrading the wiring. I've ordered a 50 amp relay and will grab power directly from the battery. For now I'll install a simple lighted rocker switch below the dash. When I have a bit more time and ambition I'll use the plunger to switch the relay. Seems a good upgrade.

I'm going to post up another thread to see if I can locate some parts. I'll also post some photos. The car almost completely original in and out and is in great shape. Needed some serious cleaning to make the exterior halfway presentable but I'm making progress.

Thanks again for the expertise!