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I have a 2003 E150. i've replaced the alternator twice already for the same reason. the battery dies because it is not charging at low engine speeds. what could be the cause of the same malfunction of the alternator? I replaced it first after 2 years, the replacement gave way just now, and i replaced it again.
new battery 12.6v, before replacement of alternator idle voltage 12v. fast engine speed 13V. when i replaced the alternator and recharged the battery, battery 12.6v no load, idle 13.6, high rev 14v. i opened up the old alternator and the ic and diodes were burned out.
My diagrams show the alternator has the built in or built on regulator. It also shows a orange/lightblue leaving the alternator going to a brown fusible link, and then runs over and ties into the large black/orange wire. The orange/lightblue is the sensing wire, and is were the regulator samples the system voltage, and decides how much the alternator puts out.
I would check the plug were this wire plugs into the alternator. I would also check this wire all along it's length, making sure it's ok with no corrosion. If you want to experiment, you could unplug this wire and then run a jumper from this terminal(terminal "A") over directly to the battery, and then see what voltages you get at the battery at idle.
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