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Hey guys, I am working on a John Deere GX85, It will start and run but when you either engage the mower deck or try to drive, The motor dies. What electronic modules do these mowers have on them that could cause this, and where are they located ?

Thanks !!

Probably someone tried bypassing the seat switch.

For circuit diagram you need john deere technical manual TM1491 dated 07-1999 as there three versions of the wiring harness.

Just to follow up with this, I found the issue. After testing all the safety switches they were fine but, On the transmission, there is a sensor that threads into the transmission and has 2 purple wires connected to it, I unplugged the clip and inserted a jumper wire and everything works fine now. What does that sensor do ? Should I just leave it or replace that sensor ?

Thanks.

Okay that is your neutral safety switch. The following wiring diagram is for a RX75 but should be the same for RX85. When jumper the switch wires you activated the Neutral Start relay which disconnected the seat switch circuit and PTO. But note once the PTO is turn on if the seat switch circuit is shorted it still kills the engine.

StarTech said:

Okay that is your neutral safety switch. The following wiring diagram is for a RX75 but should be the same for RX85. When jumper the switch wires you activated the Neutral Start relay which disconnected the seat switch circuit and PTO. But note once the PTO is turn on if the seat switch circuit is shorted it still kills the engine.
View attachment 68895

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So it will drive now but when I try to engage the mower deck it shuts down ??

x540 said:

So it will drive now but when I try to engage the mower deck it shuts down ??

Click to expand...

This is why you need to test the PTO now to see if it is shutting the engine. If it does as I said there is a short in the seat switch circuit.

StarTech said:

This is why you need to test the PTO now to see if it is shutting the engine. If it does as I said there is a short in the seat switch circuit.

Click to expand...

Could I also use a jumper on the seat switch ?

Thanks.

So I followed the wires from the seat switch to a relay box, I disconnected the relay and it all works fine now.