Join Date: Feb 2014
Location: Grand Rapids, MI
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2002 7.3L Charging Problem
This is my first post, so I apologize if I leave out any critical info. I am new to the Powerstroke world! My truck is a 2002 7.3L, 217,000 miles.
I am having a problem where my alternator is not outputting the correct voltage. While driving the other day, after plugging in my block heater for the first time since I got the truck last week, my lights became dim, gauges died, ABS and airbag light turned on then finally all interior electronics died. The batteries were 5 years old and failed a load test at Advanced Auto Parts, so I replaced those. I also replaced the alternator with a brand new (not re-manufactured) one from Advanced Auto Parts. My batteries still will not charge while the truck is running.
With the truck off, I measure about 12.5v at the batteries after charging with a wall charger. With the truck running cold, I measure around 10v (I'm assuming because the glow plugs are on). Once it warms up, voltage goes back up to around 11v, after the glow plugs are off, and then steadily decreases as I drive. I should be seeing somewhere around 14.5v with the truck running and glow plugs off. I can't figure out what is going on. When I disconnect the red terminal on the alternator with the truck running, I measure around 3.2v to the negative terminal on the battery and chassis ground. Open circuit voltage should be 14.5v to my understanding.
Does the alternator ground through the mounting bolts to the chassis ground? Because I do not see a ground wire to go to the battery negative. Also, there is a three wire plug on top of the alternator, of which, only two wires are connected. It is like the alternator is not turning on. Do the wires on the 3-wire plug control the alternator turning on? Could I have fried a ground wire or something with the block heater? Any suggestions on what to check next would be greatly appreciated!! Thanks in advance!