Might not help but you could use your multimeter to measure ac voltage on your dynamo. Just unplug it and touch your multimeter leads to the two wires. Never heard of one putting out to much a/c voltage but anything is possible. Unless you get some kind of super high reading there I would have to believe your rectifier is no good.
YM1100D electrical issue
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careyo63
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You have a wiring harness problem also is my guess now. Donor tractor and replace the Alternator ?. Fredricks show a AL-1500. 12.v Replacement for the YM1500 The YM1500 has the same production Yrs. as your YM1100 77-82 and the YM1500 75-79. My guess the way they change it over is easy. Then you can use the AL-1220 with a built in Reg. also. Then you don't have to worry about the Harness problems. Straight voltage to the battery.
ponytug
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With the tractor off,what is the voltage across the battery?
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kwms56
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Okay, the mystery deepens. Just took a reading on ACV from the two wires coming from the generator: 9.54 VAC. This was done with my very best multimeter, so I feel like it's pretty accurate. At the same time, the VDC reading on my dash-mount meter shows 17.2 VDC.
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kwms56
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After sitting overnight, 12.7 VDC.
careyo63
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Battery sounds in good condition. To get 17.2 V on a 12V. SYS. Wiring!! Your lucky to get 15V with a Alt.. My prev. guess also Harness! Bad ground on something?