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Faunsdale, AL | Your alternator isn’t getting the signal to make it excite.
Test voltage in the small plug on the tractor side of the alternator regulator harness. Can also probe in the back of it with it plugged up. You should find one wire (reference wire) with 12 volts at all times. Other wire is the signal/excite wire and should be hot with key switch on and dead with it off (engine stopped).
Check the rest of the installation by starting the engine. Plug that little harness back into the alternator. Rev up to about 1500 rpm and jump from big output stud on back of alternator to each of the small wires in that little plug in turn. You can use any piece of insulated wire with the ends stripped back a little. Just hold one end on the output stud where the big cable hooks to alternator and push the other end into the back of the plug on the alternator. I don’t think any of them use a weather pack plug so you should be able to back probe it.
One will be the reference wire so nothing happens when you touch positive source to positive source. The signal wire may/should make a small spark when you jump it and alternator should immediately build up voltage and work until you shut tractor down. Note, once alternator excites, it will backfeed 12 volts into the excite wire from the alternator end, so testing with it plugged in with tractor running and alternator putting out doesn’t diagnose anything about the tractor side of the wiring.
Edited by ccjersey 4/23/2024 16:50
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4555 Alternator issue
