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  1. #1
    New Member
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    Oct 2012
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    7
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    Near Jamestown, ny
    Tractor
    ford 3550 blt

    Default JD 420 electrical problem

    Hi all,

    Looking for some help on a electrical problem that is driving me nuts.

    Tractor is a Mid 80's JD 420 lawn tractor with front and rear pto's and a front loader.

    My problem is with the pto circuits. I am not getting any dash lights and no power to the pto's. the pto work when hot wired. I have the factory manual and am following the flow chart. Problem is the flow chart keeps telling me that different wires are open. How ever when I check these wires 1 by 1 they check out good.

    The oil press and charge light work good.

    When checking the pto switch power, it says to check for power at switch terminal with yellow and purple. Voltage IS present with key on. Book says that means Purple wire to pto switch is open. It is NOT open when checked with a dvom.
    Power test at TDC module, it says ck power at pink and purple wire terminal. Voltage IS present. Book says purple wire to pto light switch is open. Again, it is NOT open.

    This next test at the 20 amp fuse. I have voltage on both sides. Book says to replace pink wire to 8 pin connector. Again I check this wire and it is good. NOT open. This wiring harness has not been hacked and is in good shape.
    All 3 of the starter safety switches work, the 2 pto switches and the transmission neutral switch.
    The only safety switch that is not there is the seat switch. Missing for years ever since I have owned it.

    I do have a question on the seat circuit. The 2 pink wires that go to the missing switch have continuity between the pink wires even though there is no jumper wire. That doesn't look right to me. But I checked both wires by ending the loom and they are fine.

    I am guessing the Time delay control module may be bad. But I don't like to quests and throw parts at a problem.

    This is the early model with the external grounds and the grounds test good.

    Anyone out there willing to help? I will run any test suggested.
    Also, does the TDC do screwy things like this when they go bad?

    This tractor is in nice shape. I know I can hot wire the switches, but I am going to sell this since I bought a bigger tractor and would like to have all the safety equipment working.

    Thanks, Joe W

    Oldsrip@yahoo.com

  2. #2
    Veteran Member JerryK's Avatar
    Join Date
    Feb 2004
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    1,274
    Location
    Vanderbilt, Michigan, USeh?
    Tractor
    Mahindra 5035, JD 2240, 420

    Default Re: JD 420 electrical problem

    Hard to trouble shoot, that control module has it's hooks into the whole wiring. One thing to remember, having voltage does not mean you have enough current to bring in a coil/relay/etc. You have to check for voltage and trouble shoot while you are actually trying to bring the PTO in while the tractor is running just like you were trying to operate it. My 420 had problems with the fuse holders after the tractor had some years on it. The fuses would loose connection due to the connectors withing the fuse holder loosing spring connection, heat, and probably years of vibration. I had to replace the main 20 amp fuse holder after putting up with it for years. My 420 is a later year, over 475000 serial, and only have the front PTO. Good luck, Jerry...

  3. #3
    New Member
    Join Date
    Oct 2012
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    7
    Location
    Near Jamestown, ny
    Tractor
    ford 3550 blt

    Default Re: JD 420 electrical problem

    Hi Jerry,

    Thanks for the info. The 20 amp fuse holder has been replaced and upgraded.
    It was suggested that I upload a copy of the schematic. If I can figure out how I will do that.

    One thing I didn't mention is that I can hear the relay in the module click on when I turn the pto switch on.
    But it seems power is not getting from the module to the pto.

    How about that seat switch. With the jumper removed, should I have continuity between both pink wires?
    It seems to me that they should be open until either the seat switch is activated or a jumper used in its place?

    I didn't have time to look into it yesterday. May have some time today.

    I am far from the worlds best electrical guy, but can usually figure things out if I have a schematic. Very frustrating at the moment. I will continue to check all the connections.

    Thanks, Joe

  4. #4
    Veteran Member JerryK's Avatar
    Join Date
    Feb 2004
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    1,274
    Location
    Vanderbilt, Michigan, USeh?
    Tractor
    Mahindra 5035, JD 2240, 420

    Default Re: JD 420 electrical problem

    I jumpered my seat out back in '02, as per the print below between the RED and PINK wire. I had my control module out once when I rebuilt my battery tray to allow using a GM style battery mount with side terminal battery. You might pull your battery and pan then take a look at the connector going to the module. You might have gotten some battery acid/fumies down in that area under the battery. If not, then I would suggest trying to take the module apart and looks for small cracks in the solder around components soldered to the circuit board. It is common for cracks to appear due to heating/cooling/vibration/etc. in circuit boards... especialy large components or connector pins...

  5. #5
    New Member
    Join Date
    Oct 2012
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    7
    Location
    Near Jamestown, ny
    Tractor
    ford 3550 blt

    Default Re: JD 420 electrical problem

    Quote Originally Posted by JerryK View Post
    I jumpered my seat out back in '02, as per the print below between the RED and PINK wire. I had my control module out once when I rebuilt my battery tray to allow using a GM style battery mount with side terminal battery. You might pull your battery and pan then take a look at the connector going to the module. You might have gotten some battery acid/fumies down in that area under the battery. If not, then I would suggest trying to take the module apart and looks for small cracks in the solder around components soldered to the circuit board. It is common for cracks to appear due to heating/cooling/vibration/etc. in circuit boards... especialy large components or connector pins...
    Hi Jerry,

    That is the same schematic I am working with. Thanks for posting that.
    I see what you did with the RED and Pink wires. By doing it that way you seem to have bypassed the TDC box. I tested the PINK to PINK, but that is after the TDC box.
    I will have to look into that. I didn't mess with it yesterday and today doesn't look good. So I will report back as soon as I get a chance to look at it.
    thanks for your help.

    Have a safe and happy 4th of July.

    Joe

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