Converting from Magneto to Battery Ignition

[953 nut 54,907]

A few weeks ago a member requested guidance in rewiring a 312-8 from the magneto ignition system on his Kohler M12 to a battery ignition system on a replacement engine and retain the safety switch functions. I began looking at possible methods of accomplishing his goal and found that there were two basic systems depending on the ignition switch type.

The 300 and 400 series Wheel Horses can be broken down to three groups when it comes to basic wiring. 1985 and 1986 all had K series Kohler engines with battery powered ignition systems with the exception of the 1986 308-8 which was a Magnum M-8 and the 1986 420LSE which was Kohler powered with a M-20. After all, this is Wheel Horse so there had to be exceptions. 1987 to 1997 were M series Kohlers and 1998 and later were Kohler Command powered.

All 300 and 400 models that were equipped with Kohler Magnum engines from 1987 to 1991 used the 103991-ignition switch and from 1992 to 1997 they all used the 116338-ignition switch. These two switches are not interchangeable and the method of transitioning from magneto ignition to battery ignition was a bit different depending on the ignition switch. (see switches below)

The goal was to avoid having to rewire the tractor while retaining the safety switches. The seat and PTO switches on a magneto ignition system are wired in series while the seat and PTO switches are wired in parallel in a battery ignition system. With the use of inexpensive automotive 5 pin relays, I was able to come up with a satisfactory solution that isn’t too involved.

Utilizing this method the engine will shut off whenever the operator leaves the seat regardless of the PTO switch position. This is a bit inconvenient but it is the only way I could find without rewiring the safety switches. The wire gauge used on the safety switches of a magneto ignition tractor are too small to be used for a battery powered safety switch system.

First, we will cover the modifications needed for the 1987 to 1991 300 and 400 series that have a 103991 ignition switch.

Since the Ignition switch does not have power to the "A" (accessory) terminal in the Start position we will use one relay to provide 12 volts to the ignition coil during Start. This will be done by running a wire from the small purple wire on the solenoid to the relay terminals 30 and 85 to finish 12 volts coming from terminal 87 of the start relay to the ignition coil + when the relay closes. Placing the ignition switch will provide power to the small purple wire actuating the relay and passing power to the ignition coil if the operator is in the seat.

The Dark Blue wire from the PTO switch that presently goes to the magneto coil will be disconnected from the PTO switch and eliminated. A wire from the seat switch light green side will be connected to relay terminal 86 to allow the relay to close if the operator is in seat during Start. (see start diagram)

Once the engine starts and the key is released the white (sometimes pink) wire from the voltage regulator to the ignition switch “I” terminal will have voltage to it.

When the key is released to the Run position the second relay will provide 12 volts to the ignition coil. The white wire from the voltage regulator to the ignition switch will be spliced into and connected to relay terminals 30 and 85. The ignition coil and light green seat switch wires will be the same as the other relay.   (see run diagram and combined diagrams)

On the later 1992 to 1997 models with the 116338-ignition switch a single relay can be used because the “L” (light/accessory) terminal has power in the Start and run positions. This wiring would be the same as the run diagram.

 

 

[WHX?? 48,696]

Thank you Richard I just somewhat had this problem with rewiring Alice the C-120. PO went the other way tho ... from a battery ign. to mag. powered M-12. Thankfully he had changed out the ign switches and since the safeties were hit and miss so I nixed them.   

 

[ebinmaine 67,106]

@953 nut

Thanks for posting this!