LawnRanger came up with this diagnostic sequence which I found very good. I modified it a little. Hope this helps you.
Electrical* problems can be very easy or very difficult, depending on four things.
1. * How well you understand basic electricity.
2. *What tools you have and know how to use.
3. *How well you follow directions.
4. *You don't overlook or assume anything and verify everything.
Remember we cannot see what you are doing. *You are our eyes, ears and fingers in solving this problem. *You must be as accurate as you can when you report back. *The two basic tools we will ask you to use are a test light and a multi-meter. *If you have an assistant when going through these tests it would be very helpful. *These steps work the best when done in order, so please don't jump around. *Now let's solve this problem.
First, check the fuse(s), check battery connections for corrosion (clean if necessary) and *voltage - above 12.5 volts should be good.*
First, thanks for taking the time to help! I checked the fuse which is fine. Let me know if any of the readings seem screwy. I have an antique tester. I checked the battery connections for corrosion and tightness. All looked good. I checked the battery voltage and was coming in under 12 volts, at about 10.8.
Second, check for power from the battery to one of the large terminals on the solenoid. *One of the wires is connected directly to the battery and has power all the time so one of the large terminals should light a test light or show 12 volts on a meter at all times.*
I checked the battery into the solenoid and it came in at 10.8 volts
Third, *check for power at the small terminal of the solenoid while depressing the clutch/brake pedal and holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch). If your solenoid is a four wire solenoid, check both small wire terminals as one is ground and the other is power from the ignition switch.
It is a four terminal. I had my wife sit on the mower while I checked. It was a 194 millivolts.
Fourth, check for power on the other large terminal of the solenoid while holding the key in the start position (you may need an assistant to sit in the seat to override the safety switch).*
NEGATIVE 12.2 volts
Fifth, check for power at the starter while holding the key in the start position (assistant again).*
0 volts
Sixth, check your ground circuit back to the battery.
OK