Electrical Issue? I’m out of ideas....

[AimmeAshley]

Hi,

I have a John Deere D100 that I’m trying to troubleshoot and is driving me insane. This D100 has a Briggs and Stratton 31C777 engine that I think has an electrical issue.

Right now, I have NO SPARK with the kill wire attached to a new ignition coil. I ended up buying a new ignition coil (thinking that was the issue) and gapped/installed it correctly.

Without the kill wire attached, I can get the mower to start up and have the PTO engage. I can also move forward and reverse correctly. Basically, there doesn’t seem to be any issues with the mower running WITHOUT the kill wire attached to the ignition coil. Once I connect the kill wire back to the ignition coil, I won’t be able to get a spark anymore.

I used a multimeter to verify that the brake switch, PTO switch, RIS switch, and seat switch are functioning correctly. The only thing I haven’t verified is the ”RIO Switch” but I’m not sure if that exists in the John Deere D100 that I have. I can’t seem to find where that switch is. In the schematic, the “RIO Switch” seems to control “Forward/Neutral” and “reverse“ but I can’t physically find it.

What I find odd, is once I install the ignition coil, the kill tab is already grounded. Is this normal? If that’s the case, I don’t see how the mower will ever get spark if the kill tab is already grounded and having the kill wire connected.

I’d love some help. Thank you.

 

[Rivets]

Have you checked the key switch? Can you post the model number off the ID tag, so we can lookup the schematic.

 

[AimmeAshley]

Hi,

Yes, I checked the ignition switch by fully unplugging it. I checked all positions. Without anything attached to it and at the Run position, M and G are open.

The model number of the D100 is:

1GXD100ELBB138416

Btw, is the kill wire tab at the ignition coil normally supposed to grounded to the engine chassis?

 

[Rivets]

No, the kill wire should go back through the key switch. If you mean neutral safety switch, by RIO, it is located on the transmission, normally on top.

 

[bertsmobile1]

And remember that the kill circuit is a ground circuit
As such if any of the kill wires are shorting to ground then the circuit is activated.
I generally use short jumpers to bypass the individual switches, one at a time.
Often it works out that while a switch works when you depress the plunger with your finger, when activated by the mower it does not .
If bypassing all of the switches yields the same result, then there has to be a ground short.
To find the ground short you can either use long jumpers tp connect from one plug socket to the next or disconnect the kill wire at the coil then work back through the wiring with a test lamp hooked up to the + terminal on the battery, cause you are looking for a ground .
Prime suspect will be the kill wire between the mower to engine plug & the coil

 

[AimmeAshley]

Sorry if I misspoke, but I meant the kill tab on the ignition coil itself. No one has given me an answer yet, but is that supposed to be grounded as soon as I bolt it on? That kill tab is measuring a short to ground as soon as I bolt it on.

I don’t see an actual switch on the transmission. All I see are two little circular nubs that stick up. They’re connected to a wire harness that is removable. Are the circular nubs the RIO switch?

I can certainly try removing each switch and testing them again, but I’m not sure if any of the switches are bad.

Right now I know that the kill wire is nudged between the engine chassis and starting motor, so maybe I can try to disconnect the starting motor and check the wire all the way through to make sure it’s not inadvertently grounding itself.

 

[dougand3]

Without the kill wire attached, I can get the mower to start up and have the PTO engage. I can also move forward and reverse correctly. Basically, there doesn’t seem to be any issues with the mower running WITHOUT the kill wire attached to the ignition coil. Once I connect the kill wire back to the ignition coil, I won’t be able to get a spark anymore.

Without anything attached to it and at the Run position, M and G are open.

If M and G are closed in the OFF position, then ign switch is working.
Bet the kill wire is grounded inappropiately (insulation worn off) between coil tab and ign switch.
I'd examine the length of the M wire on key switch to the coil tab.

No one has given me an answer yet, but is that supposed to be grounded as soon as I bolt it on? That kill tab is measuring a short to ground as soon as I bolt it on.

If key OFF = yes grounded. If Key ON = no ground. If yes, bet the kill wire is grounded before key switch = bad.

 

[Fish]

On these engines, every time the flywheel turns, it produces a spark, the 12 volt system is out of the loop, and if 12 volts is introduced to this tab, it will destroy the coil. So if the engine runs fine without the coil hooked up, then your coil is fine, and your trouble is somewhere else.
When the coil is grounded by the switch/system, then the engine shuts off.

 

[Rivets]

Those two ”nubs” are the connection points for the transmission switch.

 

[Telesis]

The RIO [Reverse Implement Option] switch is the yellow push button on the dash just below the throttle lever on the left. If you have the blades engaged and you shift to reverse, the moment you press the drive pedal, the engine will shut off. You must press the yellow RIO button before pressing the drive pedal in order to back up with the blades engaged.

FWIW!