1994 Taurus GL died on highway

[shorod]

I'd also like to add that the battery is a critical part of the charging system. It acts not only as a reservoir for the electrical system, but also as a filter to smooth the ripple from the rectified AC. Without the battery, the alternator output is a noisy rectified signal. That noise is not good on the car's computer or many of the sensitive sensors in a modern automobile.

The alternator test from years ago of disconnecting the battery and seeing if the car will run just off the alternator is not a good thing on a modern computerized automobile.

-Rod

[Celly]

ok, it's probably a stupid question, do I unplug the cables from the B+ and A terminals when I am testing the voltage? not sure where to stick the leads without unplugging them

[Selectron]

The A terminal will always have battery voltage on it, even with the ignition switched off and key removed, so for that one, you can just unplug the connector (ignition switched off) and measure the voltage inside the end of the loose connector, then plug it back in when that's done.

For the B+, that connector bolts onto a large stud, so you can measure the voltage on the stud. There will probably be a large, flexible rubber weatherproofing boot over it, which you can pull off and slide back up the cable an inch or two while you measure the voltage (ignition on and engine running for that one). When finished, switch off the engine and slide the boot back into place. If the weatherproofing boot isn't an easily detachable one, then trace the wire back until you reach the first accessible connector, and measure the voltage at that point instead.

[Celly]

ok here are the results,
Battery Voltage is at 12.2 now..

on Terminal A, the cables has the battery voltage, zero on the alternator side

on Terminal B+ with the engine running idle, voltage reads 11.7-11.8

[Selectron]

The 12.2 V reading at terminal A confirms that the connection between battery and terminal is intact, so the regulator does have current available to feed to the field coil.

What's not so good is that the 11.7V (which should be 14.2V) which you are reading at the B+ terminal won't actually be coming from the alternator - you will effectively be reading the battery voltage, because the B+ connects via a fuse to the battery positive terminal (the voltage has reduced from 12.2V to 11.7V though because the battery is delivering current, with the engine now running). So that tells us that the connection between B+ and battery is intact, but the alternator is producing little or no output current - so you do definitely have an alternator fault rather than a wiring fault.

The fault could be any one (or more) of a number of things - you may have a faulty regulator, faulty field coil, faulty brushes, or faulty stator coil. I doubt there's a fault in the rectifier, because a problem with the diodes for one phase would reduce the output significantly but it wouldn't reduce it to zero output, so I doubt that, unless it's been a catastrophic failure.

What would you be thinking of doing next? I'm thinking back to what you said in your opening post about the car not having much value left in it. In that case you may not want to put a new alternator on it, but if you would be thinking about a trip to the boneyard to pick up a replacement then you're clear to do that now because as it stands, your present alternator is useless.

With an older car, and one which I didn't want to spend much money on, I'd pick one up from the boneyard. I might take a look at the brushes first to see if that was the problem, and consider replacing those if a new set wasn't too expensive, but I wouldn't go beyond that - I wouldn't be buying a brand new regulator or diode pack to fit onto an old alternator.

Hmmm, I just remembered something. Remember you did briefly see 14.4V a couple of times when revving the engine? That could tie in with worn brushes - no longer making continuous contact with the field coil slip rings, but touching briefly due to vibration when revving the engine. That's by no means certain though. I don't think I have any information on replacing the brushes in the Taurus, but I'll check. Meantime, you could have a think about that and let me know what you might want to do next.

[oasisgod]

In adition to what he said I once had a very simular problem with an oldsmobile. Even though there two different manufactures the charging system is very simular. It turned out what was getting me was a dirty alternator plug. The plug you see with 3 or four wires going to the alternator you should pop off and examine for signs of corrosion or dirt. If it appears dirty spray some elecrical cleaner in there and try to shine it up. That plug is what energizes the coils no coil juice = no alternator output. Check it out take you 5 minutes.

good luck and tell us what fixed the problem for you

[Celly]

I finally managed to take off the alternator, unscrewed all the mounting screws but it wouldn't budge. Took it to nearest advanced auto parts and they told me it's dead. I looked up eBay and ordered a used one for around $37 shipping included, not too bad I assume considering new ones are about 150-200ish, next challenge would be putting the alternator on, the serpentine belt's gonna be a bitch to get back on, the auto tensioner is way deep inside to reach..
Anyway, thank you very much once again for all the help, hope this problem is over once I get the new alternator on hehe of course naturally something else would go wrong with this old car soon after one thing is fixed, can't wait for the next surprise...