Hey hef I got a good one. 120 Deere straight not c model. The excite circuit going to d+ on alternator hooked to alternator has 23 volts. Same voltage with it unhooked. The ECM monitors the voltage on excite wire and thinks engine is running. Thus supplying ground to the safety relay preventing starter from engaging. That's an over simplified version. There is a resistor it ohms out at 200 ohms not positive of spec. If I use test light in place or in addition to resistor the computer sees low enough voltage and turns battery light on and does close starter safety valve. Could this just be a bad alternator not enough resistance to pull voltage down so computer doesn't think it's running. New alternator shows additional wire with built in resistor....
John Deere 200LC won’t crank I have a problem with a 200LC John Deere I need help with. It won’t crank and when you turn the key off after trying to crank it the battery relay stays energized. I have determined the alt shut down relay and starter protection relay are staying energized thru a ground signal coming from the... HeavyEquipmentForums See posts # 10 & 11, confirms your suspicion of a bad alternator.