Basic Facts.
Car threw a P0174 code last week (I believe this is unrelated to this issue, but more info is better).

Wife has 2002 Ford Taurus with 3.0L OHV non-Flex engine.

Yesterday, my wife drove 40 minutes to work and parked. The temp out was about 38 degrees during the day. She parked in an underground garage (45 degrees) and when she came out at lunch, the car would not start and from what she described, it seemed like the starter was not engaging.

I drove up there and got there a few hours later (after a stop). Put my key in and it started right up. Drove it 40 miles home with no problems. I stopped to run in and grab my daughter from daycare, leaving the flashers on. I was only in the school 4 minutes and when I came out, the car was sluggish to start (like a weak battery). I shut the flashers off, it started and I drove home (a 4 minute drive from the school).

So. Dead Battery right?? No. Batter was manufactured in April 2008 but tested good at AdvanceAuto on their tester. I had it charged (3 hour slow charge) while I yanked the alternator.

Alternator tested good at both the Advanced and O'Reilly's testers (putting out 14.4v according to the O'Reilly tester).

I buy a new 72 month battery (just in case the battery was bad under load).
So, I buy a new serpentine belt (100k on the car) and reinstall the alternator.

I reassemble. Since I have some electrical experience (building tube guitar amplifiers), I removed the B+ (battery lead) and used a voltmeter to test (assuming I would see a 14.4 or close DC voltage on that terminal).

NOTHING...

My wife jumped in it and went around the block. The battery light came on the dash (it KNOWS it is not charging I assume).

So.. I am left to wonder.... Is the Alternator really bad (and failing under a real load, but PASSING under the O'Reilly machine load)?

The other thing is maybe there is something wrong with the 3 pin connector (or whatever those wires go to) that is preventing the
alternator from generating the charging voltage.

I am assuming one of those pins is a ground (unless it is grounded through the body of the alternator itself).

In motorcycles, I would expect the alternator to have three wires or terminals that would go to the 3 terminals of the selenium rectifier.
I do not know what to look for on this Taurus.


Any thoughts?? I would appreciate any help.

 

I am assuming the B+ wire to which you are referring is the hot lead coming off the alternator. If so, it should be hot anytime the battery is connected to the vehicle. If not, check all the fuses especially the Maxi fuses in the fuse box under the hood. Not sure if ECM controls the alternator fields on this car , but in any case the hot lead needs to connect to the battery. I believe the hot lead connects to the post on the underhood fuse block. and the battery supply also connects to that same fuse block terminal.

 

Hey check the output wire from the alternator with a volt meter while engine is running.. If it is putting out the 14.4 as oreilly's said a quick fix is to cut and splice a new piece of wire and run to battery hot terminal, if not the alternator is bad, oreilly's machine only tests In perfect conditions, and is known to throw false positives.. You can find a wiring diagram online to find the output wire if your unsure of which one it is, alternator should ground through the case on this car, sounds to me like the internal voltage regulator may be bad in it... Also you may check while key on engine off that one wire to the alternator is hot this is your signal wire to the voltage regulator... Hope this helps...