Ignition problems (maybe)

[RLB1963]

Just bought a 85 300 D turbo with 168k original for $350 and put almost 40k miles on it. I have to choke it to stop running. It got to the point it needed a battery. It cranks super slow and wont start. The starter spins the motor but not fast enough to kick it in. When I jump the starter from underneath, starter armature hits flywheel nicely and spins slowly. The same goes for the purple wires by the battery, run a jumper slow turn. Either neutral safety switch, ignition switch, or ignition tumblers. I am not a mechanic, but can do a lot thanks to this forum and you tube. How do I tell if its nss or ignition switch, or tumblers. Btw good compression and fuel delivery. Help plz.

[Diseasel300]

You might want to post this in Diesel Discussion. You'll get WAY more help there. This forum gets swamped with all of the political crap in the other forum.

If the starter spins slowly when you jump the relay, you could have problems with your power wiring (poor connection, bad ground, etc), a failing starter motor, or a low battery charge. You have checked the battery charge right?

Failing voltage regulators on the alternators are very common. If you get the car started, test the charging voltage to make sure your alternator is working properly. A weak battery will crank slooooooooooooow on a diesel.

[Sugar Bear]

If it does anything when turning the key, these "Either neutral safety switch, ignition switch, or ignition tumblers" are all ok.
As suggested check the battery charge and condition. What does it do when jumped by another vehicle? Does it spin faster?
It sounds as though you are willing to "dive in", if that is the case try to borrow a decent multimeter/voltage tester or buy a Craftsman at about $20-30.

Try a jump start with good cables and let us know the result. Good luck!!!