Here's a letter from a reader who persisted even though the shop foreman told him the alternator was OK.

1989 Ford Ranger Pickup Truck 6 Cy, Fuel Injected Manual Transmission


1. The Charging System would sometimes cut out, and even when it was "working" I noticed that the Alternator Gauge would gradually read lower, and lower, over a period of a few months, and turning on Lights would drop it even lower.

2. I took the Truck to the Shop, several times, as things got worse, and each time their Tester said the Electrical System was "OK".

3. Finally, the Charging System stopped working altogether.

4. I took the Truck to the Shop again, and this time they said the Alternator was bad, and installed a Rebuilt Alternator.

5. I parked the Truck, while I went on a 2 day trip, and when I got back the Battery was dead.

6. I measured the Current, with a Multimeter, with the Engine and all Electrical Devices off, and found a 2.5 Amp continuous drain on the Battery.

7. I traced the source of the current drain, by pulling Connectors, Fuses, etc., and found that if I pulled one of the two Connectors on the Alternator, the current drain went away.

8. I took the Truck back to the Shop, they checked it again, and said their Tester said the Electrical System was "OK", it's not a problem with the Alternator they had installed, and that it's an Electrical System problem, and I need to take the Truck to an Automotive Electrical Shop.

9. I went on the Net, found Bob Hewitt's very excellent Automotive Web Site, and sent him an Email explaining the problem, and asking him if the Alternator could be bad, but the Shop's "Tester" say it's good.

10: Bob sent me a very detailed reply, explaining that it certainly could, if the Connector that I had pulled was the Battery (BAT) Connector. Bob further explained that one of the Diodes inside the Alternator could be shorted, causing the drain on the Battery, but the Alternator would still put out 12 Volts, and therefor pass the Voltage Output Test, however it could not put out full Current, and would fail the Current Load Test, IF the Shop actually ran that Test. Bob also gave me instructions on measuring the Resistance at the Alternator Connector to determine if the Alternator had this problem.

11. "Armed" with this information, I went back to the Shop, and although it took making a CAD Drawing, on the Computer, showing the Parts, Wiring, and Connections involved, along with a detailed Written Explanation, plus talking to 6 people, including the Shop Manager, over a period of about 5 days, to finally convince the Shop that this problem could exist, they finally agreed to replace the Alternator again (as they said that they had no way to really Test for this problem, in the existing Alternator).

12. The final solution: YES - it WAS the Rebuilt Alternator, and when they replaced the Alternator again, the problem went away - full output Voltage and Current - and no more Battery drain.

My Comments and Observations - and things to watch out for.

1. It's obvious that the Original Alternator was going bad over a period of time, but the Shop's Tester said it was OK, and it's obvious that the 1st Rebuilt Alternator was also bad, but the Shop's Tester said it was also OK. This tells me that, in all these cases, the Shop was running only the Voltage Output Test, and was not running the Current Load Test - watch out for this, when a Shop tells you that their "Tester" says the Electrical System is OK, but you are still having problems.

2. As to the 1st Rebuilt Alternator, the Shop Manager told me that the Technician who installed it, had changed the positions of the Connectors on the Alternator, from Side Mounted to Rear Mounted (he called it something like "Clocking the Connectors" - I didn't get the exact word), and that this could have also caused the problem. On the 2nd Rebuilt Alternator (the one that worked), they did not do this. So another thing to watch out for.

3. Make sure you're well prepared with all the necessary "firepower", i.e., the info and knowledge (like you get from Bob Hewitt) before going back to the Shop to try to convince them that they didn't do the work correctly. In my case, had I not had this "firepower" to confront them with, the situation would have been horrible. Shop #1 wouldn't have installed another Alternator, and I would have gone to an Auto Electric Shop (Shop #2), just to have them tell me that Shop #1 had put in a bad Alternator, then there would be the dispute between Shop #1 and Shop #2 as to who was "right", and I probably would never have gotten back the $$$ I had paid to Shop #2 to tell me that Shop #1 was really responsible.

4. It is apparent that some of the Automotive Technicians know how to run a Tester, take the Readings, and perform whatever Service Work is recommended according to what the Readings say, but they accept whatever the Tester says as "Absolute Truth", and they really don't understand what the Tester is really testing for, or what the Readings really mean, or how to interpret any Variations in the Readings (and change the Tests accordingly), or what could be wrong with the Part they are replacing. So, if you are continually having problems, don't necessarily accept the first thing, the first Tech tells you as "Gospel", and don't be afraid to talk to as many people at the Shop as necessary, including the Manager, or his Manager, etc., until you find someone who really understands what is going on, as to the problem you are having.

Best Regards, Bill

Back to Brother Bob's Home Page

Copyright © 1997 by Bob Hewitt - All rights reserved