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Scag STT52A-CH25 has been starting for months after several attempts turning key to start. Now I can't get it to start without jumping the solenoid. I've replaced the ignition switch, ign. relay, and solenoid. I get full (12.8V) battery voltage, with key on start position, on green/white wire from relay up to the engine harness. With light blue wire going to the solenoid connected, I read 0 volts with key to start. Blue wire test no resistance from harness. A red wire going into the engine is connected to same pin with blue at connector. I've cleaned engine ground and replaced terminal ends on wires. I've ground tested white wire at the same connector (on engine harness) and all safety switches seem good. I tested PTO switch with ohm meter - good, tested seat and park brake - good, and could not get to switches on control arms. (They tested good through white wire ground test). I've not found any rodent damage to wiring nor corroded connections. I feel like this is a wiring problem and short of replacing the interface module, I don't know what else to look for. ANY suggestions are welcome ...

I would test the ignition switch without it connected to anything, use an ohm meter or use jumper with 12volts to the correct terminal on the switch , turn to on position and verify power, then start position and watch your test light , I've seen bad ignition switches straight out of the box. If everything passes then start looking at harness connections / wires.

Bertrrr said:

I would test the ignition switch without it connected to anything, use an ohm meter or use jumper with 12volts to the correct terminal on the switch , turn to on position and verify power, then start position and watch your test light , I've seen bad ignition switches straight out of the box. If everything passes then start looking at harness connections / wires.

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I have 12.8V from the switch through the ignition relay to the engine pigtail. That's where it ends.

Unplug the pigtail and use a jumper straight to the starter solenoid small terminal , maybe your pigtail connection is corroded

Bertrrr said:

Unplug the pigtail and use a jumper straight to the starter solenoid small terminal , maybe your pigtail connection is corroded

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I tried that and was surprised that I got no results. I will try again today with better wire connection.

Hayward51 said:

I tried that and was surprised that I got no results. I will try again today with better wire connection.

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I tried jumper wire from harness to solenoid again and I lose power when I connect to the tab. ?? It's like it grounds out when I touch 12V to it. I changed the solenoid back to the old one and got the same results.

With so many items replaced and never tested the old ones, I would make sure every wire at the key switch is connected proper. Use reading glasses if needed. I do..... If one wire is not in the correct spot.......

Pull the spark plug/s. See if it cranks/spins over the engine.

Were these new parts all OEM?

slomo said:

With so many items replaced and never tested the old ones, I would make sure every wire at the key switch is connected proper. Use reading glasses if needed. I do..... If one wire is not in the correct spot.......

Pull the spark plug/s. See if it cranks/spins over the engine.

Were these new parts all OEM?

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The first part I replaced was the start relay. It was a used part I had and assumed was good. Key switch was OEM. Solenoid was not.

You may want to pull the starter and bench test with 12volts , it should Jump and spin freely if not , bad starter,
Clamp it down good b/c it will Jump off the bench when you hook the voltage

Bertrrr said:

You may want to pull the starter and bench test with 12volts , it should Jump and spin freely if not , bad starter,
Clamp it down good b/c it will Jump off the bench when you hook the voltage

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Thanks, Bertrrr. Could that be what's killing the battery voltage when I attach the trigger wire ? Even though I can jump the solenoid and start it ?

Personally I would carrying mower to a confident shop...As electrical work can be messy if you don't know what you are doing. I had guys to spend several hundred dollars trying fix a problem to only bring the equipment in and I find a fifty cent terminal bad. of course the cost of terminals is going up as every thing else.

If you jump ( bypass ) the solenoid and it kicks off , your starter is good but either your solenoid is bad or you have a bad connection - wire causing an open circuit or your ignition switch is not working right.

Bertrrr said:

If you jump ( bypass ) the solenoid and it kicks off , your starter is good but either your solenoid is bad or you have a bad connection - wire causing an open circuit or your ignition switch is not working right.

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I have changed out the solenoid and it made no difference. What I don't understand, when I connect the trigger wire to the solenoid, it grounds out immediately.??
BTW - I've also changed the wallowed out ignition switch.

Check what you're calling the " trigger"wire for ground,
The wire should have 12 volts on it in the start position , nothing while in Run or off , start there, Possibly you have the wrong wire as Trigger wire ? or landing it on the wrong terminal

Mower side wiring

As for the engine wiring there is only 187 different Kohler CH25 engines. Most uses a solenoid shift starter but a few used an starter with a remote solenoid.

StarTech said:

Mower side wiring
View attachment 69384
As for the engine wiring there is only 187 different Kohler CH25 engines. Most uses a solenoid shift starter but a few used an starter with a remote solenoid.

Click to expand...

Bertrrr said:

Check what you're calling the " trigger"wire for ground,
The wire should have 12 volts on it in the start position , nothing while in Run or off , start there, Possibly you have the wrong wire as Trigger wire ? or landing it on the wrong terminal

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I have full battery voltage (12.8V) in start position on green/white wire from the relay to the engine connector. I see it there until I touch it to the tab on solenoid.

StarTech said:

Mower side wiring
View attachment 69384
As for the engine wiring there is only 187 different Kohler CH25 engines. Most uses a solenoid shift starter but a few used an starter with a remote solenoid.

Click to expand...

Mine is STT52A-25CH / 6700284 with solenoid attached to starter.

You say it won't start, but does it turn over? In the past, did the starter struggle to turn the engine over? Does it try to turn over, but doesn't seem to have the power to do it? If this is happening, pull the spark plug. If it cranks Ok now, the problem could be that the valves need adjusting. Most of these more modern engines have compression release built into the cam shaft to leave the exhaust valve open slightly as the piston goes up, and then the valve closes during last part of the compression cycle. This makes the engine easier to crank. If the exhaust valve clearance to the push rod is too much the remains closed and there is too much compression for the starter. Adjust the valves precisely. This is a 4 cycle, right? I've seen this before and a new starter won't solve it. Rope pulls are also very hard under these circumstances.

rhkraft said:

You say it won't start, but does it turn over? In the past, did the starter struggle to turn the engine over? Does it try to turn over, but doesn't seem to have the power to do it? If this is happening, pull the spark plug. If it cranks Ok now, the problem could be that the valves need adjusting. Most of these more modern engines have compression release built into the cam shaft to leave the exhaust valve open slightly as the piston goes up, and then the valve closes during last part of the compression cycle. This makes the engine easier to crank. If the exhaust valve clearance to the push rod is too much the remains closed and there is too much compression for the starter. Adjust the valves precisely. This is a 4 cycle, right? I've seen this before and a new starter won't solve it. Rope pulls are also very hard under these circumstances.

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It cranks and starts fine when I jump the solenoid. I'm still tracing the wiring problem.