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Alternator Question

Posted: Fri May 31, 2019 10:50 pm
by pgp1999
I have a 2001 Sable. Recently the positive cable coming off the alternator came off the eyelet connector because it was corroded. I cleaned off the eyelet connector and reattached the wire to the alternator. I checked the voltage at the connector/nut on the alternator with key/engine off and also in the middle of the cable and I get battery voltage (which is currently low @ 10.1v because the alt was disconnected), however when I check voltage when the car is running, I get 18.2v at the alternator connector/nut, but only 9.8v at the battery. Is it possible that the alternator is bad or is it possibly the cable? I find it strange that the voltage is the same at the battery and at the alternator with key/engine off, but then when it's running I don't get the same 18.2v reading at the battery that I get at the alternator. Does that indicate the wiring is at fault? I would think that the wire is good considering I get the same voltage at both sides of the cable when the car is off. Any thoughts?

Re: Alternator Question

Posted: Sat Jun 01, 2019 9:42 am
by Magus732
Is the battery charging while you drive? If so, there's nothing wrong with the wiring. The "low voltage" warning light - the little red battery light on the dashboard - will come on once the voltage drops too low; the starter needs at least 9.6 volts to operate. Until it comes on, just check it every so often to make sure the cable remains in place.

And, for the record, with the engine running, voltage at the battery should be 14-15 volts. Any higher and it means you've likely got a bad voltage regulator. Since you've admitted disconnecting the battery, it's no surprise it's reading 9.8 volts; the battery voltage dropped after you first started the engine, and should come back up after the battery has a chance to recharge, which can takes several minutes, or even, if the battery's low enough, several hours. You can't expect it to jump up in a few seconds. :?

Re: Alternator Question

Posted: Sat Jun 01, 2019 6:11 pm
by ChartGuy
The Alt post and the battery + should be the same volts within a few mili volts. It is #6 wire and quite heavy, same as the battery cable. Any difference between the volts from one end of the wire to the other indicates a bad wire. Also check to see that the mega fuse is good.

-chart-

Re: Alternator Question

Posted: Sun Jun 02, 2019 9:02 am
by Magus732
I agree it shouldn't drop more than a few millivolts down the wire, but if the battery's been allowed to discharge, it won't read the same as the alternator until it bumps back up; the cable might, but the battery itself won't. Not to mention, no part of the system should be reading 18.2 volts at all; that's way too high to be a correct reading, so I'm suspicious anyway.
Check the amperage in the battery before you replace anything; that'll give you a better picture of the battery's condition, and whether or not it's being charged. If the positive cable is still charging the battery, the wire's likely just a little worn, and you don't have to replace it until it stops charging. In that case, Chart is correct; check the mega fuse - under the hood, on the far left side of the power distribution box - or the mini fuse - in the aforementioned underhood fusebox; should be fuse # 26 under the hood - to see if one of them need replaced; that could be the cause of your low voltage reading.

Re: Alternator Question

Posted: Sun Jun 02, 2019 7:51 pm
by pgp1999
Is the regulator internal to the alternator? Would the alt need replaced if the regulator is bad? I know 18v is overcharge but I wasn't sure if the reg was bumping it up since the battery was below 10v.

Re: Alternator Question

Posted: Mon Jun 03, 2019 8:08 am
by Magus732
It might be internal, it might not. There are two types of alternators used on the fourth-gen Taurus/Sable. One has an external regulator, the other one an internal one. Unfortunately, you'll have to take the alternator off the car to do anything with either one.

Re: Alternator Question

Posted: Wed Jun 05, 2019 9:27 pm
by pgp1999
After charging up the battery and reinstalling, I'm still getting 18 volts from the alternator, however while running the battery is still showing it's voltage which was 12.xx. The mega fuse and the #26 alternator fuse is fine.