# Electrical problem: Sears lawn tractor wont start



## mikecutgrass (Mar 18, 2020)

I apologize for basic question.

I have sears 247.288852 21HP mower with briggs motor. The motor would click and try to turn with no luck. It starts right up when jumped. Time for a new battery anyway but new battery, fully charged, does mostly the same thing. So its like it doesnt have enought current to turn the motor.

Solenoid is 3 pole. I have approx 12vdc on one side and when trying to start its only showing about 6vdc on the other side when I turn the key. I did not disconnect any wires when I did this test. The fuse is good at the solenoid.

The alternator shows 0 resistance to ground from each lead and about 1.5 ohms between the two leads. Im assuming this tells me the alternator AND the diode is good. 

Does that low voltage at the solenoid mean I have a bad one or did I not test it correctly since I didnt disconnect the other wires (safeties?) connected to it?

I dont know what else I need to check and would be grateful to anyone that can point me in the right direction and maybe help me a troubleshoot a bit before I replace something that doesnt need replacing!


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## Bob Driver (Nov 1, 2017)

Before you start throwing parts at it, check for a bad ground. Usually both the battery and a remote solenoid are "frame grounded". A corroded ground will cause a huge voltage drop. Take a set of jumper cables and connect *BOTH LEADS* on one end to the negative terminal at the battery. On the other end... Connect one lead to the engine block, connect the other lead to the mounting bolts/legs on the remote solenoid and then test crank. You're creating a "return ground" circuit to the negative side of the battery. If the voltage drop goes away you've got a bad ground. You can clean the ground contacts at the frame, but I hate frame grounds and just replace the jumper cables with permanent ground wires (battery to block --- Block to solenoid mount), they are just going to eventually corrode again because the OEM was trying to save $3 worth of ground wire when they built the machine

If a frame ground doesn't help that huge voltage drop, you need to find if the drop is coming at the solenoid or the starter.
1) Disconnect the main wire *at the starter* and crank. Measure at the main starter wire. If you still have that huge drop, the drop is coming from the solenoid.
2) Reconnect the main wire at the starter and crank. Measure at the main starter wire. If you still have that huge drop, the drop is coming from the starter

You also need to check the positive wire coming from the battery to the solenoid for corrosion. Check voltage at the battery terminal end... Check voltage at solenoid terminal. More than .5VDC drop is a corroded cable.


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## GreenerDays (Apr 3, 2020)

Do what Bob suggested, I just had the similar problem and it was a corroded positive cable from battery to solenoid.. check the ohms on all those wires. Bet that's the problem.


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