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Do you have a test light or a voltmeter?
Ok, at the alternators small connector. With the key on does the yellow wire have power to ground?
right the small yellow wire that goes to the 3 port connector does that wire have power?
Ok, good does the big wire at the bolt lug have power too?
Who tested the alternator?
Ok start the engine and tell me the voltage at the big lug again.
So the lug at the back of the alternator reads 12.1?
Ok with it running check the yellow again. What do you get?
Check it with the 3 prong plug hooked to the alternator and it running or did you do that?
Ok, because you just verified all the wiring is working as it should. The alternator even if its new or your original one is not working
Does the 3 pole connector appear to be damaged in any way?
At the prong for the yellow wire does it have 12 volts?
Ok this is different. Start the engine. Hook one end of the voltmeter to battery negative at the battery. Hook the other end to a clean spot on the engine. The reading will be very low but I need to know exatly what it reads.
You have tested all of the wiring. It all passes.
Wiring is perfect. Even the connector. Theres nothing else to do except get a good alternator...
Switch alternator brands maybe one from NAPA
Hello, backing up, with key ON only. does the charge light come on the dash?, if so what happens after you start the engine to the light?
Did the LIGHT ever come on in the past with key on? Yours should have a light as well as a guage as you mentioned
so the light DID work just prior to this problem correct?
I still want to reconfirm... does the light come on with key ON only, NOT started and running?
sorrry. its important to know, forget with it running etc, go to the truck, turn key to ON only, does the light on dash come on for the battery.charging?
The thing is the LIGHT MUST work with key ON position only. If the buld were to fail OR the fuse for the light blow? the alternator will NOT charge, The light must work with key ON> If it is not? then need to check bulb as well as fuse # 15 a 7.5 amp fuse in the INSIDE fuse box. Lets say the fuse blew? it will NOT charge. If all is ok? then go to parts store and get a new plug assembly. They are sold aftermarket, Plugs were a big problem on these. You said you tested and changed alternator so lets rule that out, Its either the bulb? fuse for the bulb ? or the plugs which you can buy easily at most any parts store. Here is the wiring diagram link I have attached. I promise without the light working with key on? this indicates a problem with bulb or fuse and by regulator design? it will not charge unless light is in working order,. Hard to explain
sry for the delay. I would be sure you have 12 volts to the fuse and change fuse just to be sure . LMk thanks