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My GX85, ID M0GX85X112764, blows the 30 amp fuse next to the battery each time the key is put in the on position. I've looked for bare spots in the + wire and haven't been able to find any damage on the insulation. How can i check components to see if the short is in the ignition system or charging system?
Thanks-

So it blows the fuse without starting the engine - running or starter turning? correct?, just putting the key into the on position?

Start by isolating some components like the starter, pto, charging system until it stops blowing the fuse, then you can proceed with checking for the shorts.

1. ) Check stator for short to ground.
2.) Check starter /solenoid for short. (stuck in a position that wants current, lots of current
3.) Check coil(s) for short/damaged - resistance readings
4.) Check all switches for shorts. These may be
5.) Check safety interlock electronics for short or blown items

Pull the plug off the back of the ignition switch, fuse blows problem in wiring,
Fuse does not blow, problem with the switch.
You can get a circuit breaker that plugs into a blade fuse holder if the cost of fuses is getting a bit much.
Unlike car ignition switches mower switches have a ground terminal ( to turn off the magneto) so they can go short internally.

JD318420 said:

So it blows the fuse without starting the engine - running or starter turning? correct?, just putting the key into the on position?

Start by isolating some components like the starter, pto, charging system until it stops blowing the fuse, then you can proceed with checking for the shorts.

1. ) Check stator for short to ground.
2.) Check starter /solenoid for short. (stuck in a position that wants current, lots of current
3.) Check coil(s) for short/damaged - resistance readings
4.) Check all switches for shorts. These may be
5.) Check safety interlock electronics for short or blown items

Click to expand...

Yes, its blows a fuse when the key goes to the on position. So I went through and disconnected each item one by one: ignition coil, stator, starter, seat switch, PTO switch, RIS switch, and finally the neutral start switch (NSS). Finally the fuse did not blow when I disconnected the NSS.

I tested the NSS and found continuity between terminals when it's in neutral, no continuity in all other gears. The repair manual is difficult to understand , I think the switch is functioning correct but the description in the manual seems to say otherwise. Here's what the repair manual says: " If there is continuity between the terminals when the transaxle is in neutral, check transaxle linkage adjustment, switch installation and repeat test procedure. If the switch fails, replace"

I also tested the ignition switch according to the repair manual and it doesn't show continuity between the terminals as required by the test (see attached image). Terminal A-B and D-E have no continuity in the Run position. Terminal A-B have no continuity in the start position.

I'm thinking the problem is in the ignition switch, not the NSS.

In the on position you only have power to two items,
The fuel cut off solenoid and the alternator.
Both of these should have a plug, just near the starter motor.
Pull the plug ( S) and try again.
The NSS should only be active when the ignition is in the start position as it breaks the circuit from the battery through the ignition switch thrugh the PTO switch through the Brake switch through the NSS to the trigger terminal on the starter solenoid.

If it blows with the NSS in circuit and the ignition switch in the on position then the ignition switch is sounding suspect.
You can test this easy by making up a pair of patch leads ( small jumper leads ) to make the starter switch contacts at the plug.
Be very careful tha you do not put 12V down the magneto wire or you will fry the magneto.
It is the only conact that is closed with the switch turned off ( ground + Magneto ) .
I have the luxury of trying a known good switch, you will have to buy one to test with which is not returnable.

Follow the chart, 3 positions, off, on, start. continuity = 0 ohms - zero, if analog VOM or digital VOM, some digital VOM will sound (beep) for continuity/0 ohms. testing the post shows where there should be continuity. I usually go through the switch a bunch of times to make sure. I write down on a copy of paper what the meter shows or does.

The manual you are using has a mistake in it,
It shows exactly the same connections for on as it does for off.
Also the same connections for start as it does for run
Oviously this has to be wrong.
Two terminals must go closed when off & open all other times. This is the magneto kill wire that gets connected to ground.
To run you need power to the fuel shut off
To recharge the battery you need to connect the alternator to the battery
To power the blades you need to have power to the PTO clutch

To start you need to have power to the starter solenoid, fuel shut off solenoid and might have the alternator in circuit as well.

I don't have a factory service manual for this mower so unless you have one with a wiring diagram you are willing to scan & post on site this is as far as I can take you.
Good luck

bertsmobile1 said:

The manual you are using has a mistake in it,
It shows exactly the same connections for on as it does for off.
Also the same connections for start as it does for run
Oviously this has to be wrong.
Two terminals must go closed when off & open all other times. This is the magneto kill wire that gets connected to ground.
To run you need power to the fuel shut off
To recharge the battery you need to connect the alternator to the battery
To power the blades you need to have power to the PTO clutch

To start you need to have power to the starter solenoid, fuel shut off solenoid and might have the alternator in circuit as well.

I don't have a factory service manual for this mower so unless you have one with a wiring diagram you are willing to scan & post on site this is as far as I can take you.
Good luck

Click to expand...

Yes I agree, the manual must be wrong. I located another image from www.gatorforums.net which looks like the correct one. I've attached the image. The ignition switch passes the tests as listed.
To rule out the NSS, I put a jumper across the connector. The fuse blows when the jumper is in place and the switch is in the on position. With the jumper removed, the fuse doesn't blow. As I mentioned earlier, I've disconnected all the other electrical components one at a time and in each case the fuse still blows.
I also attached the wiring diagram for the GX85 in 3 images.

I ordered a new ignition switch but I'm not convinced it's the switch yet.

Here's the updated ignition switch image.. it did not load with my previous post.

That looks a lot better.
OK so get some wire, pull the plug off the back of the switch and bridge the C & D terminals.
IF the fuse blows then there is a problem in the wiring
If the fuse does not blow there is a problem in the switch.
Interesting way to wire a lawnmower.
SO it looks like you also have power supplied to the 2 relays from the same terminal.
Thus all of the purple wires will have 12 V through them while the mower is on except the one from the S 2 terminal to the starter solenoid
This means that you will have to check each & every purple wire of continuity to earth
And because the purple wire also supplies the + trigger to both the relays via the yellow wire you should get continuity through the trigger coil of both relays so they will need to be pulled before you do any testing or you may get a false reading .

bertsmobile1 said:

That looks a lot better.
OK so get some wire, pull the plug off the back of the switch and bridge the C & D terminals.
IF the fuse blows then there is a problem in the wiring
If the fuse does not blow there is a problem in the switch.
Interesting way to wire a lawnmower.
SO it looks like you also have power supplied to the 2 relays from the same terminal.
Thus all of the purple wires will have 12 V through them while the mower is on except the one from the S 2 terminal to the starter solenoid
This means that you will have to check each & every purple wire of continuity to earth
And because the purple wire also supplies the + trigger to both the relays via the yellow wire you should get continuity through the trigger coil of both relays so they will need to be pulled before you do any testing or you may get a false reading .

Click to expand...

OK so I finally found the purple wire coming from the NSS was pinched and shorted to the chassis. It must have happened when I replaced the belts a few weeks ago. Thanks so much for the advice, it was very helpful in tracing the problem.

Cheers.

Good to hear.
Electrical problems are always easy to fix.
Problem is finding the little buggers.
Customers alway get confused when they get a bill for $120 labour and $ 8 for parts.