Alternator failure: have put two Alternators on within the last 2 weeks second one just failed again what seems to be the problem dealerships it has to be something other than that alternator do you have any idea what it could be?

  • What does the word "dealerships" in your question mean? The lack of punctuation makes it hard to read. Commented Jun 24, 2018 at 18:36

1 Answer 1


One thing that can cause alternators to fail is poor or loose connections - alternator electronics do not like being disconnected from batteries.

If an engine is running then disconnecting the battery can cause a high voltage spike through the control electronics and rectifier damaging them. Some say disconnecting the battery is one way to check an alternator is charging - this was fine when we had generators but not with alternators.

Have a check of all the cables between the battery and the alternator - this include all the earth or grounding cables, as any loose or broken cable could cause the issue.

Edit: as Steve says, using a voltmeter to test for the voltage drop is the way to go. The voltage drop or loss is calculated from I^2 * R, so any increase in resistance from poor connections shows up.

Connect the meter between the terminals at each end of the wire and see what the reading is - loading the circuits is necessary - having all the items like lights, heated window makes the alternator produce power, or for other leads operate the starter...

  • 1
    Specifically test the "D+" lead, which is the heavy wire between the alternator and the battery. Perform a "voltage drop" test from the alternator terminal to the battery terminal. If this reads anything more than 0.5 volts, I would suspect the D+ wiring.
    – SteveRacer
    Commented Jun 27, 2018 at 1:34
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    That test is good for any of the wires, @Steveracer I’ll borrow that into the answet - thanks
    – Solar Mike
    Commented Jun 27, 2018 at 6:38
  • Borrow anytime. The trick is to teach how to do voltage drop. When I was a vocational college teacher, I used to preach hot and heavy. It's a simple concept but very difficult to explain with full understanding. But I kept the faith, and I swear this simple thing is one of the most powerful tests any tech can have in his/her arsenal.
    – SteveRacer
    Commented Jun 27, 2018 at 6:54

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