8N 12v battery drain

My 1952 8n has suddenly started draining the battery overnight. Here's what I know: It was converted to 12 volt by previous owner, but I've owned the tractor for 22 years with no electrical problems. It has started quickly every time. The battery is 720CCA and slightly more than two years old; the battery works without problems in other tractors and cars. Now, I can fully charge the battery, but it discharges overnight. I'm embarrassed to say the ammeter has never worked, and I've never pursued it because I've never had problems. Now I do. Before I do too much reinventing of the wheel, what advice can you offer in tracking down the problem?( I'm somewhat electrically challenged with anything less than 120/240, and I haven't needed to work on 12-volt stuff for at least 15 years.) I'm thinking stuck or bad contacts in regulator, but does that make sense? I also have to check for a bad wire somewhere. Other ideas? Thanks.
 
Thanks for your quick response. Delco 3-wire alternator (one big wire, two small ones together on a plug), so a built-in voltage regulator. I can pull an alternator off of one of my old Chevy parts cars to see if that helps, if you think it would be worth trying. It's an easy job at zero expense.
 
(quoted from post at 13:06:34 08/25/16) Thanks for your quick response. Delco 3-wire alternator (one big wire, two small ones together on a plug), so a built-in voltage regulator. I can pull an alternator off of one of my old Chevy parts cars to see if that helps, if you think it would be worth trying. It's an easy job at zero expense.
hat would be a fine approach. You can also connect a small 12v bulb (marker lamp, dash panel bulb, etc.) between the battery cable end and the battery post (drain will light it), then start with unplugging that alternator plug, then the big alternator wire, etc. and when bulb goes dark, you will have found the source of the drain.
 
OK, I put a test bulb between the negative battery post and the negative ground cable, and the bulb lights up. When I unplug the two-wire plug on the alternator, the light goes out. When I plug the two-wire plug back into the alternator, the light comes on again. So, at the risk of verifying my ignorance, what does that tell me? (Did I set this test up correctly?) Thanks again.
 
(quoted from post at 16:49:34 08/25/16) OK, I put a test bulb between the negative battery post and the negative ground cable, and the bulb lights up. When I unplug the two-wire plug on the alternator, the light goes out. When I plug the two-wire plug back into the alternator, the light comes on again. So, at the risk of verifying my ignorance, what does that tell me? (Did I set this test up correctly?) Thanks again.
ells me that it is time to swap one of those old Chebby alts that you spoke of.
 
Can do! I've already picked out a three-wire in a rusty old 350 V8 Nova sitting in my machine shed. I've already stolen a coil from it, and the carb is worn out, so it will never miss its alternator. I really do appreciate your expert advice.
 
One thing real quick.

That 2 spade plug. 1 wire goes to charge stud, other to ign switch thru a resistor, diode or other isolation.

IE, one soade #2 is hot all the time. If you plug that plug in backwards, it will make it drain, because #1 will see hot.

Your alt swap test is easy and free.
 

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