interceptor84 1 #1 Posted August 29, 2019 Hey everyone! I have a mid 90's 312-8 that recently started shutting down when the PTO is engaged. When I jumper the two safety switches at the PTO, it runs fine. I have since replaced both safety switches and am experiencing the problem again. I have also jumpered the the seat safety switch to take that out of the equation. My question is what else should I consider either mechanically or electronically considering the troubleshooting I have done? Thanks in advance for any direction! Share this post Link to post Share on other sites
BESTDOGEVER 218 #2 Posted August 29, 2019 If it continues to run with the switch bypassed it means something in the switch circuit has grounded out and you have the fun of trying to find the gremlin in the wiring which is better than having it stalling under load. Look at where the switch wires branch off from the main line 1 Share this post Link to post Share on other sites
AHenry014 127 #3 Posted August 29, 2019 If i were you, i would visit the wiring diagram for your tractor. The safety switch run line is specific to each model. I was going to guess seat switch but youve got that covered. Share this post Link to post Share on other sites
interceptor84 1 #4 Posted August 29, 2019 37 minutes ago, BESTDOGEVER said: If it continues to run with the switch bypassed it means something in the switch circuit has grounded out and you have the fun of trying to find the gremlin in the wiring which is better than having it stalling under load. Look at where the switch wires branch off from the main line That would make sense now that i think about it. The issue started intermittently, as in when I'd hit bumps, which leads me to belive that the wiring is missing some insulation some where and has vibrated itself into a grounded position. 1 Share this post Link to post Share on other sites
peter lena 8,655 #5 Posted August 29, 2019 think you called it on that grounding idea, its common to have a wire that has been there for years to fray or ground from vibration . you might do a search and replace a few questionable areas. at that time you could reroute and insulate to insure its function. pete Share this post Link to post Share on other sites
953 nut 55,394 #6 Posted August 29, 2019 many of the '90s models have a seat switch relay and a start relay. Under the seat there is a model number that will tell us the year and we can give you the proper wiring information. Share this post Link to post Share on other sites
interceptor84 1 #7 Posted August 30, 2019 Model number is 73362, which i think correlates to a 1995. is a bad relay a possible cause? that was something I was considering replacing to see. Share this post Link to post Share on other sites
953 nut 55,394 #8 Posted August 30, 2019 (edited) 5 hours ago, interceptor84 said: 73362, which i think correlates to a 1995. Yes, it is a 1995. In the drawing below you will see that with the key in the start or run position and an operator (or any weight) in the eat the "Seat Relay" will be energized and the ignition (yellow) wire would be removed from being grounded. I have not done this, but would suspect that in a quiet place you should be able to hear the relay open and close if the key is on and the seat is moved downward and then released. The yellow wire from the seat relay goes to the PTO switch and would not ground out the ignition in either position IF the seat switch relay is energized. Did we ever determine that nothing in the PTO switch itself isn't grounding out accidentally. Look over the drawing (page 7-25 of the Demystification Guide) and see what you think. Seems to me if you removed the "Seat Switch Relay" for testing purposes the yellow wire would be removed from ground with the PTO switch in either position. Worth a try! Edited August 30, 2019 by 953 nut 1 Share this post Link to post Share on other sites
Jeff Enders 3 #9 Posted March 1 New to your site and enjoying all the content. I am rebuilding my 312-8 and am wondering if there is a complete wiring harness for this model? When the unit was stored 2 years ago the PTO worked fine, however i got it out of storage and the PTO is shutting the engine down. So I am also (besides the other great advice) considering replacing all the wiring. Thank you, in adance. 1 Share this post Link to post Share on other sites
953 nut 55,394 #10 Posted March 1 @Jeff Enders,There are no new or reproduction wiring harnesses available but repairing yours won't be as bad as you may think. If the only problem is the PTO shutting down the engine then the seat switch or the wiring going to it is the problem. Depending on the model number there may also be a seat switch relay. Post the model number (located under the seat) and we can help you fix the problem. Share this post Link to post Share on other sites
Sparky-(Admin) 21,352 #11 Posted March 1 13 minutes ago, 953 nut said: @Jeff Enders If the only problem is the PTO shutting down the engine then the seat switch or the wiring going to it is the problem. Agree….I bet it’s the seat switch itself and for testing purposes it can be bypassed Share this post Link to post Share on other sites
Jeff Enders 3 #12 Posted March 2 Thank you to both members, I can't wait to have that first cup of coffee and hit the shop. I'll get back with you about the seat switch and relay. Also the wiring harness. Serial Number of unit. Thanks again, have a blessed day. 1 Share this post Link to post Share on other sites
ohiofarmer 3,276 #13 Posted March 3 I had that exact thing happen and it was the ignition switch itself..Replacing it cured the problem Share this post Link to post Share on other sites
Jeff Enders 3 #14 Posted March 7 Thanks 953Nut and Sparky, it was indeed the seat switch! 1 Share this post Link to post Share on other sites
