I wish I had the means with which to measure the current to each plug. I have been doing a little research on this system, I purchased the CD's from the Partsshop a while back.
Anyway, what I have learned is that the glow system uses glow plug number 1 as a current reference for the other four plugs. If the other four plugs are out of whack in comparison to number one, the comparison within the plug relay fails and the other plugs don't get the juice (I think) and the glow light on the dashboard fails also.
The corollary that I am inferring is that plug number one always gets the juice since its on the other side of the current comparison. I think I have observed this because as I begin to crank the engine when cold, one cylinder always fires, long before the others begin to get involved. I'm guessing this is cylinder number one, though I haven't confirmed this. I guess what I'm getting at here is that I think something within the glow relay circuitry has failed and doesn't allow current to flow to the other four glow plugs. Is this possible? I've seen a reed switch referred to in the repair literature.
What if two of the four "current-tested" plugs have failed? Will this be enough to upset the comparator and shut down all but number one?
Should I buy five new glow plugs or just go for the relay?
I think the battery is in good shape as I measured about 12.5VDC at the fuse strip on the relay. Yes, we do have to have hot batteries and decent compression to get these buggers going. And, as luck would have it, it has only snowed what seems like three times this season and tonight is one of them (our weather out here has been really messed up for the last two years or so) and messing with this thing in the cold and snow is no fun. I guess I shouldn't be griping too much because this car's been starting (reluctantly) without being plugged in and with what seems like one good glow plug (and a new starter if this keeps up for much longer).
Thanks for all replies.