Sometimes, the problem is in the relay. I had several relays fail on me. I suspect aluminum contacts.
The coil current on my original relays was 4 amperes. Almost pure inductive. Its hell on a cheap switch. I had some old spring-return toggle switches salvaged off old WWII military stuff, and the White Rodgers industrial contactor ( same one Wes uses ) and have had no more problems. The White Rodgers coil current is about 1/2 amp. Silver contacts. Quite a bit heavier than what I had. No way I'm gonna go back to automatic. Ive got a really good feel by now exactly when to juice my plugs and how much. And I don't have to ask my batteries to crank and glow at the same time. There is quite a a bit of thermal inertia. The colder the engine is, the more glow it's gonna need.
I'm not gonna beat a dead horse. I have electric fuel pump insuring the IP inlet is pressured up and ready to go. The first squirt of fuel oughta catch if the plugs are good and up to temperature. Now the whole thing boils down to having enough current to spin the starter motor fast enough to clear the ignition flashpoint temperature upon the "adiabatic" compression and fuel injection.
Its a physics thing...like making ice.
Water won't freeze if you can't get it below 32 degrees, neither will the fuel catch until it reaches above a critical temperature. Even though the whole cylinder may not reach ignition temperature, all it takes is one hot spot on the glow plug to start off the cascade. So, knowing I only have so much current and time to work with, I allocate my battery energy to first get the glow plugs good and hot, then use battery current to spin the starter. If the fuel injection system is working to spec, by the laws of physics, it has to catch. If it failed to catch, well I know I had compression ( by the sound of the starter motor laboring to compress the cylinder full of air ), I have to assume I got a squirt of properly atomized fuel, which should have immediately ignited upon contact with the glow plug element.
We are lucky in that we don't have that fuel-air ratio thing the gassers have, where excessively rich or lean won't catch. Ideally, we are always running lean. If we do run rich, the engine doesn't stop .. it just blows black smoke to all high heaven, as we don't light off the carbon in the fuel...the hydrogens get all the oxygens.
I guess waking up our old beasts is a lot like hunting...first, you try and miss a lot, and have to make several do-overs... For me, it used to take several tries...but by now I usually get a catch on the first compression. Saves a lot of wear and tear on the starting system. If the engine is already warm, I likely won't even need the plugs, but intake air and fuel temperatures factor in too. You get a feel for it. You've got almost a KWH of energy in the batteries. You don't want to squander it on fruitless attempts. The automatic option removes your common sense off the table.
Manually, you can destroy your glow plugs. I seriously doubt any of us here on this forum would do that. But I wouldn't put anything up to a neighbor or spouse who doesn't comprehend the physics that these beasts operate under. But a malfunctioning controller will. And leave you wondering what to heck is going on here?
The more you know about your beast, the more you will like it - primarily for me, it's pure simplicity.
