electrical trouble

I have a 47 H. Converted to 12 volt 20 years ago with a Delco alternator and magneto ignition. 5 or 6 years ago, I rewired the tractor and added a key switch and solenoid to prevent my kid and her friends from accidently cranking the engine. (I can teach my own kid to stay off the tractor, but her friends might be another story.)
This system worked fine until last week. I went to use the tractor and it acted like a dead battery. I jump started it, the alternator charged up the battery and I even got a warm restart. Next time, same thing. I checked the voltage at the battery and it was dropping to 5 or 6 volts with the key turned to crank. I had no problem replacing a 20 year old battery.
Put in the new battery, same deal. I've had an issue with the starter before, so I replaced that. Yup, same deal. The solenoid would chatter, the battery would drop to 5 or 6 volts while trying to crank.
Today I replaced the solenoid. I turned the key and the new solenoid chattered, the starter tried to crank and didn't let up until I pulled the ground wire off the battery.
The only thing I didn't try was taking the key switch out of the circuit, but when I went to reconnect the battery, there was a spark and the starter tried to crank. Even without turning the key.
Now the question; what do I do next?

Ed,

Go to the John Deere Forum and read

Re: 24 volts posts made me think of this! - Tom 43 12:41:35 01/21/12 (0)

This is a recent post. I suspect that you have bad connections somewhere in the battery cables and the solenoid may be damaged as well.

for 1, you likely have a bad connection. maybee at the ground strap to the chassie.

dropping to 5-6v on a 1 2v system trying to start is a massive drop, assuming bat not bad, then it's a bad connection or dead starter.

now.. the fact it is trying to crank and did so till you pulled the bat cable off is because due to the low voltage, the current was high and WELDED the solenoid contacts.

many times you can rap the solenoid with a screwdriver to get ti to release. some solenoids you can even take apart and clean the contacts up.. others are throw away.. etc.

soundguy

On a totally different situation and cure potential, the Alt might have a bad diode in the rectifier bridge. This will discharge the battery to the same point is short order (pun intended). A bad regulator in the alt will also do it. A bad diode in the feed to the alt to excite it (if it is not a one wire system) will also do it. Check for battery drain when it is fully charged if you see ,5 volts from a disconnected battery cable to the post, I would suspect the alt. Pull its wire off and check it again. Jim

Thanks. The ground is the only connection I haven't taken apart. I'll check that tomorrow. The battery and starter are both new. The cables are only 5 or 6 years old.

check ground strap.. and if the cables ar ethe kind with replaceable ends, remov ethem and clean up the copper to lead connection.

check that solenoid over.. may be able to salvage it..

Thanks, Soundguy! I cleaned the rusty bolt holding the ground cable to the tractor, put it together with a clean washer, charged the battery and she started right up like she should.
My first boss out of trade school told me there is nothing more annoying than a bad electrical connection. He wasn't kidding.

glad ya got it.

soundguy