Originally posted by Don
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For the wiring, it looks to me like you've got your alternator wired wrong. Here's how it should be:
S = battery Sense, and gets connected to the battery "+" terminal. You can pigtail it straight to the "BAT" terminal on the alternator, but it usually goes through a fusible link for protection. I'm not sure what current rating for the fuse is appropriate.
F or I = Field or Ignition, it's what powers the field coil during running and must be connected to a "Hot in Run" source.
L = Light, and is connected to one side of the "Volts" indicator bulb. The other side of the light is connected to a "Hot in Run, Bulb Test, or Start" source... usually the "Gages" fuse. Essentially, when the engine is running the bulb gets power to both terminals, one from the battery, the other from the alternator, so it doesn't illuminate . With the engine stopped and ignition switch on, the bulb sees 12V on the terminal connected to the Gage fuse (battery) and gets a ground through the alternator, so it lights up. Same thing if the engine is running but the alternator isn't working (broken belt, faulty alternator, etc).
Edit to add: P = not used.
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