Help me with this electrical problem...

[frischtr]

Alright, I'm stumped here...

Started mowing this afternoon, made it about 3 laps around the yard and the PT425 just dies. No lugging or sputtering, just all stop on the engine as if I turned the key off. I turned the PTO switch off, won't turn over, no clicking, nothing.

Checked the voltage to the key switch, 13 volts. Turn the key to run position, hour meter does not begin timing. So I figure it is a bad key switch. I pull it out, it meters out good. Still have 13 volts on the red hot wire in the wiring harness.

Checked PTO switch for correct continuity (to make sure it's not a false PTO cutoff situation), all good there.

I unplug all load from the key switch in the run position, which is only the hour meter, headlight switch, and fuel cutoff solenoid. Recheck voltage at the key switch in off position, 13 volts. Hook up hour meter only. Switch to run position, hour meter begins counting, 13 volts at hour meter.

Add the light switch back in (light switch in off position). Key switch to run position, and the hour meter begins counting. Turn on light switch, no lights, and hour meter stops. Now 0 volts on red hot from wiring harness, but still 13 volts at the battery itself. Turn off light switch, still 0 volts on red wire. Recycle key switch to off, then to run position again, hour meter begins counting again. So I figure bad light switch or lights. Well, the light switch meters good, headlights work when wired directly to the battery.

I left the lights unhooked, and tried messing with the fuel cutoff solenoid. When I add that load to the run position, again 0 volts at the key switch, and it won't pull in.

I have checked grounds everywhere, everything meters and seems good. Looked for shorts or continuity issues in all wiring harnesses, everything seems good. All fuses good. If I add any load in addition the hour meter, voltage at the key switch drops to 0, and hour meter stops, but battery voltage remains good at 13 volts. Never had any issues starting previously, started like a champ 10 minutes before this happened.

What else can I try?

Thanks...

 

[PTWannaHave]

Crap...! I am stumped as well!

 

[BigRol]

It could be any load you add is shorting to the meter ground which would leave you with two hots to the meter? only thing I can think of. good luck.

 

[2bON2b]

What else can I try?

Jumper key switch in same order that you were adding loads to it in your description. Sounds like switch contacts have carbon build up on them. Which also may explain how the machine cut off like it did. Loose contacts in a switching device leads to arcing which then leads to failure.

 

[frischtr]

Jumper key switch in same order that you were adding loads to it in your description. Sounds like switch contacts have carbon build up on them. Which also may explain how the machine cut off like it did. Loose contacts in a switching device leads to arcing which then leads to failure.

Yeah, I hadn't thought to bypass the switch altogether since it ohm'd /metered good, but I'll try that tomorrow.

 

[Leejohn]

I know you said you check the grounds, but you should recheck them.

After thinking about it after I posted a bad ground wouldn't just shut the engine down when running, so like was said before the key switch.

 

[frischtr]

Bypassing the key switch altogether doesn't help, same issues... Battery is strong, when wired directly to the starter motor, it cranks away.

 

[marrt]

This sounds like a bad safety switch. Now, I'm not aware of any safety switches on the PT. However, if the PTO switch is on, the tractor won't start (if I remember correctly). Maybe something to consider. I assume you already checked the fuses?

 

[Baby Grand]

I had a fusible link that was partially fused. If you moved the wire, the circuit would close. Move it a little more and it would open. Drove me crazy trying to diagnose why the tractor would shut down while in use, or start up on one day but not on another. Finally found it while checking resistance of all the components in the starting circuit. Was holding the link in my hand and it checked okay, then accidentally bent one of the wires and the meter read open.

 

[frischtr]

All switches, fuses, and wiring ohm good. Any load wired directly to the battery works, but if I use the factory wiring harness/connectors from the rear to the front, I get nothing (despite the fact that I have excellent continuity).

Every time I try something, it points to one thing, but then that thing will check out good, but points to something else, etc, until I end up back at the beginning.

Could it somehow be the voltage regulator?