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Discussion Starter #1
This weekend I started a project to install a 2000RPM rear PTO on my 1990 420. Most of the work was at the back of the tractor, as expected. It all went pretty smooth up until I went to test it. As I didn't have the tins on I jumped the seat safety with a paperclip. I do not have a wiring kit for my rear PTO clutch yet, but I grounded it at the mounting bolt for the clutch arrestment bracket thing and ran a wire up the control tower from the other lead off the clutch. The plan was to just to touch it to the battery positive terminal to test functionality, and that went just fine. The clutch kicked on, the rear PTO began to spin, and no horrible noises were heard, hooray! Except as I moved back around to the front of the tractor to shut it down, the seat-safety wire vibrated off the gas tank and the paperclip I used to jump it arced on the frame, this shut the tractor down immediately. I checked and found I blew the 3amp fuse. No biggie, slapped a 5 in there cause that's all I had, and went to fire it back up and got nothing. No crank at all.

Since then I've been crawling all over the dang thing trying to figure out what went wrong. I'm pretty new to this tractor and it's also my first JD, but reading the forums here I found wiring diagrams and some useful tips of things to look at. However I've not come to any luck in fixing the no crank condition. What I've been noting is that I don't have 12v at any of the safeties I found except the seat switch wire. There is no voltage on the purple wires at the neutral switch (This is the one on the go-lever in the dash, correct?) There is no voltage on the purple wires on the brake safety switch. There is no voltage on the purple wire leads from the key switch either, but I did confirm the key switch is opening/closing circuits as appropriate. Ultimately this means no voltage on the purple wire at the starter. However if I give 12V to the purple wire connection at the starter the starter cranks fine and I can even start the tractor if the key is in the run position. However I cannot energize the front PTO, I get nothing from it at all using the switch.

Now all in all I'm not completely lost, I can start this tractor and I'm sure I can find a way to energize the front PTO and get back to mowing, but I'd like it to work correctly and not as the result of me rigging it up to work. I found a little circuit board under the battery, I think it's called a timer control or something like that. I visually inspected all the traces on the board, the resistors on the board, and all the other components looking for something obviously burnt up, but found nothing. I don't know what else to do except rig this dude up the wrong way. Please help me not do that.
 

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Here is the wiring excerpt that pertains to the engine cranking:
318 Starting circuit.JPG

Use a voltmeter and verify you have voltage around this loop, starting at the 20 amp fuse and continuing through all the safety contacts of the various switches. If you do not yet have the rear PTO switch and wiring in place, there will be a jumper from the #730 purple wire to the #720 purple wire at X5. The wires in the loop shown above are the ONLY wires that are involved in the starter motor actuation.

The seat switch and why shorting that wire caused the 3 amp fuse to blow is best seen in this other wiring excerpt:
ignition diagram 318.JPG

The seat switch gets its power from the #800 pink wire that comes from the F2 fuse and the #500 red wire that connects to the #800 wire at the X23 pin 5 of the TDCM connector (this is the sense input to the TDCM that runs the battery discharge lamp control.) The other side of the seat switch is an input to the TDCM at X22 pin 9 through the #810 pink wire. Even if the seat switch is not present, the ignition can still be enabled for starting and running if there is voltage present at TDCM X23 pin 7, originating at wire #710 from the brake switch. So make your measurements and let us know what you find...

Chuck
 

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Discussion Starter #4
Got it! The front PTO switch didn’t have power. There was only one connector hooked up to the switch, the second connector (the two hole connector with purple and yellow wires) had dropped off. Only the three-hole connector with blue wires was hooked to the switch. While I hadn’t hooked up the rear PTO yet, I had installed the switch. Must have knocked the connector off the front PTO switch when installing the second switch. Since I didn’t have familiarity with the wiring, I though the disconnected second connector for the front PTO switch was there waiting for the rear switch to be installed, so I left it off.

Anyway, here’s where I’m at now.
259615


Couldn’t get the driveshaft you extend into the PTO, so I’m gonna drop the tiller again and work on that. Any tips for hooking/unhooking a three-point? I’m bad at it and pretty much exhausted myself wrestling it on today.
 

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I made a dolly to set my tiller on. I have a 30 hydraulic with 12 inch extension and can move it around easy. Others have used Harbor Freight dollies to set it on.
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