Think you are onto something. It seems to be the correct 4-position switch but it may be faulty: it goes like this:
Position 0 - key out
Position 1 - ignition on
Position 2 against spring - all electrics cut out incl. fuel gauge and all warning lights
Position 3 - starter cranks
So I'm guessing that either the switch is faulty in Position 2, or there's a 'short' somewhere between the switch and the glowplugs. As the wiring to the glowplugs *appears* to be via an uninsulated plate attached to the bulkhead, this may be the cause of the problem - a lashup by a previous owner!
Chapgrill
Hmmm....... uninsulated plate huh?
Is there a coil of wire on it? If not he's taken it off.
I think your position 2 IS the GLOW stage of the key. It sounds good. That's what it is supposed to do.
Check that a terminal (possibly numbered '50') goes live in key position 2
A stout wire from that terminal of the IGN switch should go to your insulated plate, through the coil, then to Plug number 4 at the back of the engine.
Two small wires should go from (one from each end of) the coil to the Glow warning lamp.
In your case are you saying there is NO BALLAST RESISTOR?
If that is so, then your series glowplugs may have been exposed to 12 volts every start-up, and I don't think they can stand that for long. One of them has probably burned out - OPEN circuit.
Test them. Take one wire off each plug before testing.
Each plug must show continuity low ohms resistance.
If the plug shows infinite resistance it's burned out, and NONE of them will heat up.
CharlesY