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Alternator killer strikes again!

Here’s the lowdown:

'98 Ford Explorer Sport

Nov. 07 - check engine light comes on, battery not charging sufficiently; alternator replaced

Jan. 08 - check engine light comes on, battery not charging sufficiently; alternator replaced

July 12, 08 - check engine light comes on, ABS light comes on, battery not charging sufficiently; alternator replaced

July 12, 08 - new alternator makes it about 10 miles before the charging light comes on, #$%@!

Question: The chances of getting 3 bad alternators in a row seem slim to none. Thus, if the alternator is working properly, something in between the alternator and battery is draining the current. The battery and starter both test good. I checked the resistance of the circuit at the battery leads and it was around 1200 ohms. This sounds pretty reasonable, considering a 12V battery would lead to about 10A of current running through the system without taking into account the electrical system, power steering, brakes, etc. The original sound system is still in the car. All the fuses were checked for shorts.

I have taken it to a corporate service shop, and they can’t tell me anything. At this point, I am pretty much on my own.

How can I test the individual electronic components? I have a multimeter, but I don’t know what kind of resistances to expect from the components?



If your getting all these alternators from Pepboys or the likes… yes they all could be bad, but unlikely.

When is it time to take it to a reputable shop and have it checked out? This is not hightech system difficult to diagnose.

Parts swapping is way more expensive than paying for diagnosing.

I’m not sure where you’re measuring resistance, but it should 0 Ohms between the battery positive post and the alternator and 0 Ohms between the negative battery post and the body and engine. If you got 1200 Ohms at any of these points, you’ve got a corrosion problem.

… thanks, i’ll check it.

There may be a problem with the wiring to the alternator that is causing the trouble. I recommend you check the voltage of the wires on the back of the alternator while the trouble is happening along with the main output. Most systems will need to have 12 volts on those wires while running.

I assume you checked the resistance between the battery connections. If so, that method of testing will work but a better test is to do a current check. To see if there is a current drain problem you want to do a current flow test rather than a resistance check. You need to set your meter up to check current, disconnect the negative battery lead and place the meter in series with the negative battery lead and the battery post. The car should be set so it is just as it would be if you left it parked overnight, nothing should be on. Some things may need a little time to got into a sleep mode so you may have to wait for a few minutes for the systems to do that after power is hooked up. If there is more than 80 milliamps of current draw measured then you need to start pulling fuses to see which leg is causing a problem. Remember to let things go back to sleep if you activate them by replacing a fuse.

One possible thing that could be happening is if the battery sense lead is shorted to ground this would make the alternator produce full output. If the alternator is getting real hot this may be the problem.

Have you replaced the battery? A bad battery will eat alternators. I found this out the hard way while trying to nurse a 6 year old battery “one more year”. Once I replaced my battery my alternators stopped burning up. Have the battery checked at an auto store. It is usually free.

I’ll second this one… I guy from Autozone told me they have a 40% return rate on rebuilt alternators. IMHO, the “Lifetime” units aren’t any better, just a n insurance policy against future failure.


The chances of getting 3 bad alternators in a row is near zero, reman or not. I’ve bought countless alternators from AutoZone, O’Reillys, etc. and never had a problem.

What I would consider would be this:
The possibility of an erratic alternator warning light on the dashboard. The circuit through the little red light must be complete whenever the key is on or the alternator will not charge. The alternator is an exciteable one and this means if the circuit has a hiccup (bulb contact maybe) the alternator will not produce.

Bad wire splice (unlikely) or possibly a burnt/corroded fusible link connector between the alternator and battery + terminal. I think (not sure off the top of my head) that there are 2 fusible links in this circuit.

My gut feeling would be the latter. And believe it or not, most problems that appear to be complicated on the surface often turn out to be relatively simple in nature.

Whenever in doubt about the alternator, turn the key to the RUN position (inoperative engine) and touch the tip of a small screwdriver to the alternator pulley. You should feel a magnetic attraction in the pulley. If you feel the magnetic pull and still get the code then the problem is more than likely the circuit between the alt. and the battery rather than dash light circuit.
And of course, if you do not feel a magnetic pull then glance inside the vehicle and make sure that little red light is glowing.