418-A charging question(s)

[cod 121]

Recently picked up a 418-A and I’m slowly working on repair/replacing worn out parts as I go.  The beast runs fine but I’m having a problem charging the battery and I’m wondering if there is a way to test the rectifier to see if it is bad.  Unfortunately I am not an electrical wizard so I’d rather ask for help before I go off half cocked.  So far I’ve measured the AC voltage from the stator and I’m getting around 30 – 32 volts AC at idle so I think the stator is okay.  I’ve cleaned all of the connections on both the rectifier and its plug and then I’ve cleaned all of the connections between the rectifier, the ignition switch and all the battery connections.  I’ve also tried to see if any of the wires and connectors were bad by testing them with an ohm meter but so far they all seem fine with 0 resistance.  I did find that the 25amp fuse for the charging circuit was bad so I replaced that and on the connector that connects to the back of the ignition switch, the lower right hand female plug (with a black and white wire) looked slightly melted. I replaced the connector with a new one.

After all this I reinstalled the battery and fired it off to see if I was getting more than 12.5 volt DC to the battery but no dice and unfortunately now the ignition key won’t kill the engine unless I completely close the throttle.

 

So any suggestions would be greatly appreciated.

 

Steve

 

PS  Right after I bought it home I replaced the ignition switch as the old one was rather worn out and while the replacement matched the old one with the same 6 lugs, in the same exact positions, I’d like to think it isn’t the problem.

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418-A uses a Kohler M18QS-24510 with 15 amp regulated charging system and magneto ignition.

 

There should be a terminal on the back of the switch marked M for magneto. The ignition switch needs to ground that terminal through a G terminal which is tied to the chassis somewhere to shut the engine off. Perhaps the engine is being grounded through the throttle cable. Check the engine to battery grounds and add another if necessary. Perhaps that is why it is not charging also.

 

Now I see the ignition switch description does not have a ground terminal so the switch relies on the metal switch housing bolted to the chassis metal to provide the ground if this is the case. If it has 6 terminals one of them should be a ground.

 

Here is a service bulletin published in 1987 when the Magnum's first came out.

 

Operator manual with wiring diagram if you need it

This is titled a 1986 manual but also listed for 1987 models by Toro. I need to check that out.

 

Garry

[cod 121]

Thanks Garry.  I'll print off the diagram and check the ground(s).  The battery reads 12.7 volts DC with the engine off so at least there's more than 4 volts.

 

Steve

[cod 121]

Just a follow up, as it turns out that the "new" igintion switch was actually the wrong one, so I exchanged it for the correct part, replaced the negative battery cable, ruined a wire wheel cleaning grounds and I suspect I'll smell like dielectric grease for a day or two but it's charging now.  Voltmeter shows 14.5 and that's good enough for me.

 

 

Steve