Riding Mower Electrical Problem?

Question

I have a John Deere L120 riding lawn tractor. I am a small engine mechanic but am stumped as to this problem I am having. It has an electric pto for the blade engagement, as well as a seat switch, plus a reverse mow switch. There are also the other normal safety switches. The problem I have is that clutch to engage the blades only engages when the seat switch is not depressed(not on the seat). If I start the engine, have the seat switch pushed down, the tractor runs fine. Then while still holding the seat switch down, I pull up on the switch that engages the clutch, and normally, it would engage. However it does not. Then with the engine running, seat switch pushed down(sitting on the seat), and pto switch pulled out(blades engaged), I then let go of the seat switch(get off the seat) and then the clutch engages, but right after that happens(within 2 seconds) the engine shuts off because the blades are engaged(and it thinks your not on the seat because the switch is not depressed) as a safety. I have already replaced the pto switch and the seat switch, and get the same problem. I have also bypassed almost all other switches to eliminate them as the problem. Does anyone out there have any ideas as to where I should look? I have also tried bypassing the clutch, and the same problem occurs. Any help is greatly appreciated. Thanks.

Answer 1

I do not have a diagram for that machine here, but I do know that the cause is one switch is stuck closed. Or a wire is shorted giving the same effect. A broken wire giving can also be a cause, too.



The logical reasoning is simple: All safety switches follow a simple rule.... Normally open or normally closed. You must look at the wiring diagram and it will (or should) have each switch marked NO or NC. This depends on the condition, but will be marked with no person on the seat.



So, with a NC (Normally Closed with no person on the seat), then it follows that that switch should be making contact. If NO Normally Open (with no person on the seat) then again it follows that this switch will be open circuit in the no person on the seat condition.



Okay: So we now know where we start from. Set all manual (driver operated) switches to the OFF position. Check the switches are OPEN with a multimeter set to continuity (tone on short) if fitted, or low ohms range. All readings will or should show OPEN. If not, then that switch is faulty.

Now, go round each safety switch in turn and, from the electrical drawing, determine what state that switch should be in with driver 'NOT SEATED'. Some switches will have to be open for the engine to start, and some switched will have to be closed for the engine to start. These have been eliminated, but for the average Yahoo Answers reader that is the norm. Any other state and the engine will not start as was stated.



We now come to the seat switch. This switch MUST be closed for current to flow to the PTO switch.

You must remove all wires that have by-passed switches and rest these to factory setting or you will not eliminate the bad switch or contact.



All ground wires must first be shown to be in good condition, that is: not frayed against frame or broken either externally or internally in the wiring loom, so buzz these out first for the purpose of elimination. A broken wire can be easily fixed with bullet connectors. Relays (if fitted) must first be shown to be functioning and that contacts are clean and not burned or burned closed when they should be open or vise-versa. Any power diode should be checked in the normal way for functionality.



mmalky: 50 years diagnosing and repairing large and small lawnmower engines.

Answer 2

Could be a bad or frayed wire in the circuit for the seat switch/clutch switch or loose wires at terminals/connectors from what others describe. Does the clutch switch provide a ground path for a relay? Without knowing how the circuits work or power/ground paths, I can't say what the issue might be other than to check for bad wiring or a stuck relay..if any. Call a JD dealer and ask if any common issues on them....sounds like it from other comments.



Others with similar problems..



"QUESTION: John

Used the jumper on the seat switch with no good results. Tied the brake switch down and the engine will run and the mower will go forward but as soon as the deck blade switch is pulled the engine will die."



" There May be a Bad Wire in the Seat Harness. The Problem you Described is Due to the Seat Switch Not Making Proper Connection and the Safety System Does Not Show Anyone in the Seat when you Release the Brake/Clutch or Engage the Blades. Check the Harness for the Seat Switch and Ensure there is No Bare Wires that May be Grounding the System or A Broken Wire in the Harness from the Seat Switch"

http://en.allexperts.com/q/Small-Engines-Lawn-1746/John-Deere-L120-4.htm



http://www.howtomendit.com/answers.php?id=163006

Answer 3

If none of the switches have been replaced or adjusted before this problem started then it is probably a wiring problem not a switch problem. Each wire must be followed by hand through each connection to locate the problem and then to repair it. I suspect that a wire has worn through some insulation and is grounding out. As MM mentions you need a wiring drawing for this unit. A modern wiring harness may break a wire inside the harness and inside the insulation with use. These are always a problem to locate but not too hard to repair with some butt splices. Good luck, this is a tedious problem. In the reading of your problem, you replaced a couple of switches, this would give me a suspicion that either the switch is the wrong type or it was wired wrong. Check the seat switch for the exact type and wiring against the old one.

Answer 4

John Deere Riding Mower Troubleshooting

Answer 5

John Deere L130 Wiring Diagram

Answer 6

have l120 with electric pto . pto stopped engaging. changed tpo ran for 15min. changed clutch ran for 15min and stopped. changed seat swith same thing ran 15min. that's were iam at.

Answer 7

What did you ever come up with, I am have the exact same problem, please help me 616-437-6907