I'm new here and certainly don't claim to be an expert on series landys. Also I don't want to tread on any ones toes so if I'm wrong tell me to sod off
Firstly there is a lack of info which makes it tricky so you have to make assumptions!
It's a non start!
It doesn't crank from the key.
No lights on dash. As I understand it.
External lights not working.
Sparks and smoke from ignition switch!
Battery charged
Ancillaries not working?
Cranks if solenoid bridged!
From that you can reason that the battery is hopefully ok (it will crank), alternator etc was working up until it was parked cos it's not flat and didn't break down. There is a fundamental power supply problem. A big one!
You clearly have power at the solenoid because you can bridge it to make it crank. I assume that is supplied straight from the battery like on most older cars, you don't appear to have power to any other circuits tho? Or that's what I'm reading? So there is a major power supply that goes into the car for non ignition stuff like lights and ignition stuff like dash warnings and cranking. Which isn't live! Now this is where I'm struggling, the alternator is connected to the system where? Dunno it's a series! I'd imagine either to the external solenoid to charge down the supply cable from the battery or maybe straight to the battery. It makes no odds. Because none of the circuits mentioned need the alternator etc to actually work, they don't work thru the alternator. You can remove the alternator regulator etc chuck it in the bin and the car will drive and everything should work until the batteries go flat! The only possible complication I can see is if it's got an ammeter fitted which has failed or in its long life someone has done something odd with the wiring.
I'm used to more modern cars and haven't seen a dynamo system for years, but I have converted them in the past to alternators and they really shouldn't be that complicated!
To me it's a case of ignore the alternator etc just concentrate on why it isn't cranking, it's a very fundamental power supply failure. If you trace the main supply to the ignition back towards the battery you can't not find a major power problem. It really is such a major problem when it's found you'll be kicking yourself because it was so stupid.
You just need a test light to probe along the cable at different points?
Also can't see it being an earth issue cos you can make it crank!
Hope all this makes sense. Like I said I'm no series expert so if I'm missing something please tell me