Ive been studying the wiring diagram for my Case 580se and while it doesn't appear too complicated, there is something amiss in the electrical system that I cant figure out. Everything was working until recently. Now, when I turn the key to the RUN position, the magnetic switch starts clicking and buzzing. When I keep turning the key to START position, nothing happens. Checks Ive done just make me more confused as to the root cause of the trouble: 1. REMOVE ALL EXTRA ELECTRIC STUFF : On the Magnetic switch, I disconnected the small orange 12v wire that runs from the start switch. This stops the 12v feed to the fuse panel and disables most of the electrical system. The 12v feed to the fuel flow solenoid in the bottom of the injection pump remains open when key is in RUN or START position . 2. VERIFY GOOD CONNECTION BETWEEN STARTER SW AND STARTER: I removed the start key switch from the wiring harness then checked the resistance of the wires from the start switch plug to the starter solenoid (disconnected the wire from the solenoid first). The path goes thru the neutral switch. The resistance was 0 ohms, so the connection is good. 3. VERIFY THAT STARTER SOLENOID GETS 12V. I put the start switch back on the wiring harness but left the wire disconnected at the starter solenoid. I attached a test light between the starter solenoid wire (at starter) and ground. When I turn the key to START, the 12v test light lights. This proves the switch and wires work and should cause the starter solenoid to activate but doesn't . 4. VERIFY THE SOLENOID AND STARTER ARE WORKING: I attached a remote starter switch between the big 12v lug on the starter motor and the small start terminal on the solenoid. With the key in OFF position, the engine cranks lively. With the key in RUN, the engine starts right up. 5. VERIFY THE STARTER SWITCH IS GOOD: I removed the switch and checked it with a multimeter, connections across the various terminals in the various key positions are all 0 ohms which is perfect. Then with start switch removed and the shuttle in Neutral position, I used a copper wire and jumpered across terminals on the starter switch plug: between the BAT/12v socket and the starter solenoid socket, but nothing happened. This should cause the engine to crank . What am I missing , something is wrong but I cant see it and I dont know how to further isolate the problem. My best guess at this point is that my 12v source to the electrical system isn't delivering enough current, it will light my little test lightbulb but wont power the solenoid. At least the machine starts and I can use it but I'd sure like to have the electrical system working.
If there are plugs (connectors) in the wiring harness separate them and look for corrosion.
You could verify your best guess theory by taking a long wire from the battery + straight to the start socket off your switch. This would tell you if your key switch 12V source is weak.
The issue turned out to be with the 40Amp breaker down next to the starter motor. For some reason it stopped passing sufficient current to allow anything more than the fuel solenoid to activate. For a temporary fix I wired up a 25 amp fuse as a bridge to let current pass. I ordered a new breaker from eTrailer. These 40A breakers seem to be a pretty common part so I just got a generic ‘Pollack’ brand unit for $5.60 instead of the Case breaker for $32 . I have to say that it’s pretty disappointing how this breaker failed after only 37 years of service . They sure don’t make ‘em like they used to !