318 Dies When PTO or Hydrostatic Control Lever Engaged

Robert,

Welcome to the WFM forum!

The wiring diagrams are in the technical manual for your tractor, TM1590, which is very highly recommended that you purchase for ongoing maintenance. I can send you an excerpt by e-mail of just the schematic as even it is too large to post here.

Is this a new to you tractor? Any idea if the wiring was cobbled by a prior owner? Here is a partial diagram showing the wiring around the ignition and safety switches. If the PTO is off, the seat switch does not have an effect normally.


Chuck

Chuck,

Thank you, after troubleshooting with the schematics you sent I found two problems. The first problem was with the 20A fuse holder, the fuse was good and there was voltage on both sides of the fuse holder, but only sometimes. The terminals on the wires inside the fuse holder had corrosion on them, replaced the fuse holder and that problem was fixed.

The second problem involved the seat switch. I know I stated I checked it and I did but after further troubleshooting I found that someone had added a 4" extension to the harness. The factory plug was under the rear body and the extension came out of the body to the seat. When I jumped the harness yesterday it had no effect because one of the connectors on the extension was bad.
I had to make a temporary jumper as I am ordering a new seat and switch this week.

I would say the wiring was cobbled by the previous owner or dealer.

While I was involved in the wiring issue I did take the time to clean all the wiring connectors in the battery box area trying to avoid further issues.

Thanks again, Bob

Scott, some diagnostic work is needed here. Do you have 12 volts at the small solenoid terminal when trying to start? I assume this starter has a Faston tab connector for the solenoid, similar to the smaller Yanmars in 330/332. The terminal has to be clean, and the harness connector has to make positive contact.

If you have the starter off, you can bench check it. Clamp it in a vise, so it can't jump around.
Connect +12 volts to the battery cable connector, and ground to the starter frame, using jumper cables from a charged battery. Jump across from the battery cable connector to the solenoid terminal. Normal operation is for the solenoid to shift the starter pinion, and make the starter motor spin. If you get no solenoid action, shift the ground to the other big terminal on the solenoid (the one connected to the starter motor) and jump from +12 to the solenoid terminal.

If the solenoid pulls in, the starter motor is open circuit internally. Most commonly worn brushes or a bad ground connection inside. Both repairable.

If the solenoid does not pull in, the solenoid is defective (open pull-in coil).

It's very rare that a sick starter motor can't be brought back to life with a simple brush and bushing replacement. A good auto electric shop should be able to do this for you.

I don't advise "aftermarket." What's being offered as aftermarket for Kohlers and Onans is cheap Chinese junk, and being sold non-returnable.

Hank

Scott, plan on getting a bit of electrical proficiency. Chuck Van Dusen and I are both electrical engineers who can give you some guidance, and most tractor electricals are pretty simple, both in concept and in execution.

Chuck may disagree to some extent, but my feeling is that at least half the electrical problems on these tractors are connector and other wiring problems, not component failures. It's important to diagnose first, then repair.

Most troubleshooting is done with a multimeter, a VOM (volts-ohms-milliamperes) meter. I much prefer an analog meter (with a meter movement) to a DVM (digital volt meter) for trouble-shooting because how the needle moves---smooth vs. erratic---is a major diagnostic indicator. A DVM just gives you spinning numbers. You can get a cheap analog VOM at Radio Shack for, I think $25.
Also, there are test lights that look like screwdrivers or ice picks with a bulb in the handle and a wire lead used to complete the test circuit.

I mentioned a "Faston tab" on your starter. Faston is the manufacturer's trade name for the flat tab (male) tabs that connect with curled-edge female connectors, with a hole in the tab and a click-in dimple in the female body. Manufacturer is TE (formerly Tyco). If those get corrosion inside, they'll make poor connection, and if loose, they go intermittent. The chemical I use for corrosion is Caig Deoxit D-5. There is a new article in the FAQ section on that subject. If loose, you can squeeze the curly ears some to tighten them back up.

"Loose and corroded" was what was giving me intermittent starter operation on my 330. "Diagnosis" was reaching in and wiggling the connector while trying to run the starter.
"Fix" was Deoxit and a judicious squeeze with duck-bill pliers (yes, through the rubber) to bend the ears "enough." Cost of diagnosis and repair, pennies (for the Deoxit).

Hank