Can't chase down starting circuit gremlin

[Inspectorjoe 473]

I recently bought a 1988 310-8. Nothing happens when you turn the key. The seller said it has a bad starter, The starter and solenoid are fine. Running a wire directly from the battery to the safety switch circuit terminal on the solenoid make the engine turn over and start just fine, so the problem isn't a bad ground. I bypassed all of the safety switches and the oil sentry relay, but it still doesn't turn over. The ignition switch is good (it looks pretty new).

There are two anomalies that might be a clue. From what I understand, the seat switch is not on the starting safety circuit, but is tied into one of the two PTO safety switches, and shuts off the engine if the operator leaves the seat when the PTO is engaged. On this tractor, the engine shuts down when the seat is vacated, even if the PTO is disengaged. The second is that the volt meter does not work (although I don't really see a correlation).

I'm at a dead-end. Help!

[lynnmor 7,707]

Download the Demystification Guide, page 7-13 shows the starting circuit.

[gwest_ca-(File Mod) 11,389]

Try disconnecting the wire harness at the low oil switch. The low oil relay still needs to be connected. There are special instructions for removing the switch for service so it is not damaged.

 

[953 nut 59,238]

You are holding the clutch down when attempting to stat the 310, right? You may have some corrosion on the terminals of the 30 amp fuse holder that feeds power to the ignition switch, the PTO switch and/or the 10 amp fuse holder. They live near the battery and acid fumes from the battery being charged can play havoc with them. 

As @gwest_ca said you can disconnect the five terminal plug from the engine (0nly has four wires in it) and if the oil sentry is the problem the engine should crank over. Once it starts you will need to reconnect the plug to turn  the engine off from the switch.

 

Edited July 11, 2022 by 953 nut

[peter lena 9,187]

@Inspectorjoe sounds like the  guys have given you possibilities , as you get it going , take advantage of that , and do over or replace trouble spots , corrosion , split / cracked / shorted connections are the norm . I  use cable wrap and stick on or screw on ty wrap mounts . reroute tight wiring , enhance your grounding , from battery ground cable bolt , next to battery , with added cable to corner of engine to frame , clutch pedal side , serrated washers , dielectric grease ,go from there to cooling tin rectifier mount bolts , to headlights , amperage gauge will also work like it should . verr good opportunity , to correct and upgrade , pete 

[gwest_ca-(File Mod) 11,389]

The low oil relay needs to be in the circuit or disconnect all the wiring from the relay and add a jumper between the light blue and purple wires.