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Every once in a while I would turn the key and there would be nothing, letting off on the key and trying again the starter woud crank, and engine ran. This problem became more frequent and now will not even click at the starter. When I turn the key to "ON" I hear a mild click that seems to be coming from the plug at the electronic mower clutch. I have checked all the safety switches by un-plugging one at a time and jumping the plug with a piece of wire. Also un-plugged ignition switch, mower switch, fuse block. I haven't un-plugged the mower clutch wire. I am not a major motor head, but understand the basics. What's wrong?

https://www.scag.com/OPManuals/STC/STCatOPMANTOC.html

First locate your serial number for correct manual. Check all wiring & connections by hand making sure everything is tight & secure. If no go remove battery & take to local auto parts store & ask them to load test battery. If you have a battery charger you may want to charge battery before taking in for testing. Be sure to check all ground wires & straps from engine to chassis, frame, etc. by hand. Electrical schematic is at end of manual. Let us know how it goes, thanks, Mark

My 2 cents.

Making sure all wiring connections are clean and tight is a great idea. I have a kawasaki set up and I guess you have a Kohler. I assume you still have a control module.

Jumping each safety switch might help find the problem with some but apparently not with yours. Jumping the safety wires does not ensure power is getting to the control module or coming out of the module and it is a slow process. I find it easier to check the power in and out of the module with a helper on the mower trying to start it while I have a test light at the module wiring. Might be a good idea to make sure the module connections are clean and tight too.

Check ground to frame and to motor scag harness should come together and bolt on the motor check there and ground to battery make sure it is good and clean. Check the light blue wire which is the pto wire with a test light key on clip to ground probe light blue wire look at the test light then pull the switch if it goes out and comes on switch is working correctly at the time do the Same for orange,brown,pink wires which is seat,brake,arms.

Luffydog said:

Check ground to frame and to motor scag harness should come together and bolt on the motor check there and ground to battery make sure it is good and clean. Check the light blue wire which is the pto wire with a test light key on clip to ground probe light blue wire look at the test light then pull the switch if it goes out and comes on switch is working correctly at the time do the Same for orange,brown,pink wires which is seat,brake,arms.

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You guys have been great help. I have checked connections, grounds, fuses. I used the test light to check the wires at the module. Clip to ground, I probed the lt blue wire, in "ON" position the light was on, I pulled the PTO, light went off, pushed PTO light came back on. On the orange wire, in on position the light came on, pulled PTO, light stayed on. With the brown and pink wires th light did not light in on position and didn't change when PTO pulled. Also, my module doesn't look like the one in the manual or that the SCAG dealer has. Mine is held with two screws to a panel on the left, near gas tank. It's front looks like a mouse glue trap, with the wires coming out of the "glue". But it does have the SCAG part number; "483599" on it's side. Have I done diagnostic correctly? Is module bad or is PTO bad?

When testing the wires don’t pull the pto unless your checking the light blue wire all the others have to move handles and push seat and brake also there is a relay under the key as well make sure you probe wires on the scag harness side black and yellow shield side that’s all scag harness if you probe on scag harness side and all the test pass that’s and good start that should prove the interlock safety module is working if those test are good i would go to the relay. Those are the basic and most common no starts for scag. Also check the wire to starter making sure it hasn’t came off causing you false thoughts. Make sure ground is good

Could be also the key switch itself forgot to say that.

Luffydog said:

Could be also the key switch itself forgot to say that.

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Luffydog, I got it figured out, with your help. I went back and cleaned all plugs and wire junctions with spray electrical cleaner, wiped spade ends with dielectric grease. Ran the diagnostic as you clarified in your last responce. All safety switches checked out okay. So I was looking at the relay or the PTO switch. Visited with the parts guy at my local SCAG dealer, and was going to purchase both until he quoted $70+ for the PTO switch. I got the relay for $18.00 and told him I would see him again to get the PTO switch, if this didn't fix it. He told me I was on the right track. Installed the relay and it fired right up. A buddy of mine put me onto Lawn Mower Forum, and this was my first message. I am so happy with the result and I cannot thank you for your help and direction. This is really a good neighbor group.
Your patience and responces walked me through this process, and I am ready to cut. Best Wishes Luffydog!

Your welcome glad you got it all worked out. Now you can diagnose yours when a no starts happens and you can help others along the way. Good luck and happy mowing