"As far as the solenoid, see if it clicks with just turning the key on without turning to crank. If it gets powered up with ignition, then it has to be a special solenoid that can handle constant power. The older cars that had a starter solenoid only energized with cranking
RTG, I completely misunderstood what you were saying here, but in retrospect I don't see how - as it seems very clear to me now.
I think you hit the nail on the head here - the solenoid that was burning out in the original configuration was triggered by the 'master power switch' in the vehicle. Therefore, it was constantly 'turned on' - not just when running the starter. I think you were trying to tell me that I should NOT be using a 'starter solenoid' for this purpose, but a special solenoid that is designed to be left in the 'on' state for long periods of time.
BTW, I wasn't able to listen for a click, as I'm working on this by myself (and can't hear anything from the drivers seat) - but I threw a voltmeter on the trigger wire and found it was controlled by the 'master switch'.
It looks like the same 'reliable mechanic' who said this should be a starter solenoid also wired the fourth post to ground. According to the instructions that came with the starter solenoid, thats wrong.
I've temporarily rewired it so that I don't have the 'master power switch' keeping that solenoid active all the time - but I didn't test the other trigger wire to verify that its coming from the ignition. I also removed the 'grounding' wire.
In the course of rewiring this, I took two wires that had been 'downstream' from the solenoid and connected them to the 'battery' (upstream) side of the solenoid. This made me nervous, as I don't know if there is an intermittent short somewhere on those circuits - so I put a 30A fuses in-line on those wires.
The next time I started the vehicle: I turn the ignition, the 'glow plug' light comes on, I wait for it to go away. I turn the ignition farther, and the starter runs. The vehicle won't start. I let it keep cranking for a bit, as air had gotten into my fuel lines last week, but it still won't start.
One of the 30A fuses I installed popped. I decided the wire with that fuse was probably powering the glow plugs - I heard that the plugs pull from 6A to 15A each. Its a V8, so I guess that means it could be up to 120A total. I put a 175A fuse (closest I could find) in place of the 30A fuse, and the vehicle started up.
The start was rough and smelled awful - I'm wondering if thats because I had flooded the cylinders in my previous efforts to start the vehicle without glow plugs???
One thing I still don't understand - it that wire was powering my glow plugs, why did the 'wait for glow plugs' light go OFF after a few seconds? Isn't that controlled by a temperature sensor? And if the plugs aren't getting power, wouldn't that light (if it came on at all) stay on?
So I'm not sure exactly whats on that line which blew the 30A fuse. I just know that it starts right now, the solenoid hasn't burned out yet, and that I think RTG was right all along - the solenoid was dying due to (a) being designed to be turned on for short periods of time and (b) was wired to a switch that was left on all the time.