John Deere 425 pto won't engage

We have a John Deere 425 tractor that we've been mowing with until lately when the pto quit working. It blew the 15 amp fuse which we replaced but still wouldn't engage the blades. Since the fuse was blown I thought it may have burned something else out on the board so we replaced the board and the ignition switch assembly. Still wouldn't engage the blade and the red LED on the board would not come on. We tried jumping from the battery to the solenoid and it wouldn't click in so we bought a new solenoid. I tried jumping the new solenoid and it clicked in fine but still wouldn't engage when the pto switch was pulled. We bypassed the seat switch (temporarily) and checked the brake switch which appeared to be good. Anybody got any suggestions of where to look next? I saw in another forum someone had a pto circuit diagnosis for a 425 but it was for the later version, ours is a 1994 and the test points were different. Thanks

Mary Wilson said:

.. so we replaced the board and the ignition switch assembly....so we bought a new solenoid. We bypassed the seat switch (temporarily) and checked the brake switch which appeared to be good.

Click to expand...

Wow. How much have you already spent on this problem?
Do you have a meter to test all this?
The led light is tricky. Is you serial number prior to # 070000?
The old solenoid that is now off the machine... what is the ohm reading across the two wires on the connector? This will be a low value.

You do not mention the PTO switch, can you test it? A faulty brake switch will prevent the pto from engaging.
Seat switch same thing, but if you have this securely jumpered this should not be the problem.

The PTO electrical system and the engine starting system are separate systems once the engine is running. It sounds like your engine is running but the PTO will not engage. If I am right you are checking the wrong system. You said it would not engage after you blew the fuse. To me that would indicate to me that a good possibility would be that the PTO clutch shorted out, blowing the fuse. Have you tried unplugging the PTO and applying 12V directly to the clutch. If it does not engage, your clutch is bad.

Mary Wilson said:

I tried jumping the new solenoid and it clicked in fine but still wouldn't engage when the pto switch was pulled.

Click to expand...

This is on the older version, but some of these is confusing. They made some different variations of the wiring on different S/N.
Maybe something here will help you.

Pto relay needs replaced. It's located by circuit board.

The PTO is hydraulic over electric meaning an electronic solenoid opens a hydraulic valve to allow fluid to flow and spin the implement.......are you getting power to the solenoid? The shaft could also be bent to causing it to jam up....

Mary Wilson said:

I saw in another forum someone had a pto circuit diagnosis for a 425 but it was for the later version, ours is a 1994 and the test points were different.

Click to expand...

This is an older version. The newer mowers will stop the PTO when you reverse the mower, which I think is the result of some crazy lawsuit.
If you try to print this it needs to be on 8 1/2" x 11" paper.
Remember you may have to be ON the seat, and OFF the brake for the PTO to engage. :confused2:
(Starting the engine is different.)

BBO said:

This is an older version. The newer mowers will stop the PTO when you reverse the mower, which I think is the result of some crazy lawsuit.
If you try to print this it needs to be on 8 1/2" x 11" paper.
Remember you may have to be ON the seat, and OFF the brake for the PTO to engage. :confused2:
(Starting the engine is different.)

Click to expand...

I thank all of you for your comments, mostly correct. We mowed the yard with it today finally! Here's what I did. First I replaced the board with ignition switch because I had trouble with it before so I figured it was bad. Then I ran two jumpers back from the battery (fully charged) to the solenoid and it didn't even click so I replaced it, still no go. I then took my ohm meter and my troubleshooting chart and checked all the wires in the pto circuit and couldn't find anything wrong so I replaced the pto switch and then it finally worked. All the parts I replaced were bad with the exception maybe of the circuit board and switch which I'm not sure of. Anyway, I kept the old one just in case. Again, thanks for your help.

Mary Wilson said:

.. so I replaced the pto switch and then it finally worked.

Click to expand...

I suspect the solenoid was the original problem.
For others this is under/behind the seat/fuel tank on the 425/445 mowers.


This blew the fuse and you put new fuse in which it also blew.
Then you put a 20A fuse in and it cooked the PTO switch, plus it blew the 20A also. :thumbdown:
J/K but this does happen. :ashamed:

When my 15A blew I put a 10A in to work on it. NEVER try a "larger fuse". You can start a fire that way...
I found that the mower ran fine (lights-everything) until I pulled out the switch for the PTO and it would blow the 10A instantly.
So I knew the solenoid circuit was the culprit before I ever checked it.

BTW the new solenoid for my 445 was a JD # AM878297 and it measured 8.9 ohms so it normally pulls ~ 1.5 amps.
My old solenoid was almost shorted at .5 ohms so it was trying to pull ~ 28 amps.