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I have a 2003 G100 Lawn Tractor that I bought 2 years ago. It's been running great until last week. It won't start. The local JD store gave me an electrical service manual. After trouble shooting it pointed to a bad key switch. I bought a new one. No luck. I tried another battery and no luck. Service manual said i should get battery voltage at red wire on key switch in the off position. I'm geting 12.75 V. In the run position the yellow wire is supposed to read the same. It doesn't. It drops to 0.9 V. If I disconnect the X4 motor connector the voltage jumps to 1.4 V. If I remove the battery discharge light bulb the voltage jumps to 11.85 V.Connecting the X4 connector back up drops it back to 0.9 V. With the X4 disconnected and the battery light off the hour gauge works but the oil light doesn't. Head lights will not work at all. I've checked the seat switch and brake switch and they're good. Any help wil be appreciated. Thanks, Dan

Electrical problems are fun to troubleshoot, aren't they? Start by finding all the chassis grounds, remove them, clean them down to bare metal and reinstall. This may not be a fix to your specific problem but it never hurts to make sure the path back to the battery is conductive. Make sure you find all the grounds including the negative battery post & cable. A not-so-well-known ground is in the body of the remote starter solenoid if it is a three wire solenoid.

Since you state that the mower was running fine for two years and all of the sudden it won't start, do you mean that the engine cranks but won't run or that the starter motor does not crank the engine when you turn the key to the start position?

I've tried cleaning multiple grounds. Just bought a new battery. When I turned key to run position the hour meter & both dash lights came on. Tried to crank and got a low volume groan from engine area (like a solenoid trying to kick in?). After about 5 cranks the groan stopped & the lights & meter went out. It's almost like something eventually is shorting B+ to ground. If I go out in a couple hours I'm sure the meter & lights will come on again (for a while). When I check the red wire at the key switch in off position there's 12.5 V. Turn the key to run and meter reads .5 V. Manual says there should be B+ at red wire, purple & yellow in run position. I'm totally stumped! Thanks for your input. Dan

Can you post the schematic or a link to it for me, please?

Schematic attached. When key switch is open I get 12.4 V at 211 Rred. When key switch is closed B+ should be at 400 & 401 yellow & 700 purple. I'm getting .5 -.9 V. Pull out Battery discharge bulb and it jumps to 1.4 V. Disconnect X4 and it jumps to 12.4 V. I'm sure PTO switch, brake switch, key switch & seat switch and light switch are good. ?????? Thanks.

X4 feeds the fuel solenoid. What happens when you unplug the fuel solenoid. I realize the engine will not start without fuel but recheck the voltage readings with the fuel solenoid unplugged at the solenoid. I have seen the feed wire for the solenoid shorted to ground and also lots of corrosion at the main engine harness connector so make sure to check all your connections for a clean, tight fit and verify that the feed wire for the fuel solenoid is not shorted to ground.

I will check that out when I get home. Is the fuel solenoid tough to get to? If I remember correctly, all wires coming from the X4 connector ended up routing behind some sheet metal around the engine.

dmzark said:

I will check that out when I get home. Is the fuel solenoid tough to get to? If I remember correctly, all wires coming from the X4 connector ended up routing behind some sheet metal around the engine.

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The wires sometimes go behind some sheet metal and that could be where the problem lies but you will have to verify by removing the sheet metal. Usually there is a screw or two holding the metal in place. However, for right now just unplug the fuel solenoid on the bottom of the carburetor to perform the tests. Usually a gray wire and a black wire in a white connector. Another good test while you are right there is to measure voltage to the fuel solenoid by going across the two wires with your volt meter.

Try eliminateing the solinoid completely by jumping the 2 large wires. Do this carefully as the sparks could ruin/weld the threads on the solinoid posts. By jumping, and process of elimination, you eliminate the ign switch, and the solinoid itself. The starter motor should turn/crank. If you do this with the ign switch "ON" and it cranks, it should start.

chance123 said:

Try eliminateing the solinoid completely by jumping the 2 large wires. Do this carefully as the sparks could ruin/weld the threads on the solinoid posts. By jumping, and process of elimination, you eliminate the ign switch, and the solinoid itself. The starter motor should turn/crank. If you do this with the ign switch "ON" and it cranks, it should start.

Click to expand...

What's your input about the schematic?

I spent another evening on this thing. I couldn't locate the fuel solenoid. I presume its under a large plate that covers the carb. I was apprehensive about taking it off. It looks like removing it also disassembles some parts to the carb. That scares me. It also looks like I would have to remove the entire cover on top the engine to get to it? I did disconnect X4 which goes to the fuel shut off and same things seem to happen. After a few cranks B+ drains. I discovered other things. Touching B+ right to the starting motor solenoid (S) - engine cranks! Also, the groan noise is K1 start relay trying to fire. With key in run position B+ dies immediately when I turn on headlight switch. It seems like there's a capacitor discharging somewhere. When caps drains completely B+ is gone. Then if I turn key to off it charges back up but not enough to get engine going. Might there be a capacitor in the A1 Discharge Light Module? Do you know where its located & what's in this thing? Thanks again!

If you are scared to work on your mower, you should probably take it to someone for the needed repairs.