Help! 1988 Sable Battery Not Charging

Sounds like a wiring/connection problem to me. Start at the regulator with a voltage check for the wire going to the field on the alternator and then do the same at the alternator. My guess is you have a corroded connection and that is causing your output to be low or non-existent. It goes without saying that the alternator belt is tight.

By the way, the AC belt and the alternator belt are not the same, are they??? A locked up compressor would slow down the alternator RPMs if they were.

Thanks for the suggestions. Because I have been through a miserable week with this vehicle, and have now gotten it fixed (by the grace of God ONLY BTW), I feel I need to share the rest of this experience with those who may encounter the same problem as I. As it turns out, I discovered this vehicle is equipped with an Electronic Windshield Defrost System. This is a special system used by Ford until 1992, and is no longer offered. This system employs circuitry which, when engaged via a switch on the dashboard, routes all of the alternator output from it's normal task of charging the battery, to directly powering the Windshield Defroster, for a limited period of 4 minutes or so. Well, this system apparently failed on my car (even though I never turned it on), consequently toasting my alternator. A by-product of this failure was that my wiring harness developed an 'open' circuit somewhere between the 2 wire modular plug which connects to the alternator, to the regulator, ie, this is why I was not measuring any 'field' voltage at this connector, when the car was running. No 'field' voltage in at this connector, no output from the heavy wire on the alternator, makes sense, right? On my car, the wire with no continuity was the RED one at this connector. After reviewing Chilton and ALLDATA drawings, my fix was to bypass the EWD System, here's what I did: Remember, this is MY fix, if you try this, I'm not responsible; I only wish to share information! First, please disconnect and remove the battery! Now, lie on the ground, and look underneath the passenger side, front fender, toward the top, you may have to pull the fender skirt back. You should see a relay block assembly, with some heavy wires going to it. This is the Alternator Output Control Relay module. Locate the studs marked 'BATT' and 'ALT' (probably will need a flashlight and mirror to see the markings properly, at least I did!). Take the nuts off of both these studs, put both wires on the 'ALT' stud, then replace/retighten the nut you removed. I also unplugged the two smaller wires from the relay block, and tied them back into the harness. You're done on the ground, now back to under the hood. Go to the 2-wire alternator connector, unplug from alternator. Remove the wire loom, and cut the RED wire. Splice another RED wire onto the end you just cut, the end that goes TO the alternator plug, use at least 14 AWG wire. Put some electrical tape onto the old wire end, and tuck it into the harnessing. Run the new wire along the existing harnessing, dressing into place as you go. This wire need to end up in the area of the voltage regulator, leave a little extra length for the next step. Next, locate the wire on the regulator connector marked 'S'. Cut this wire, leaving enough length to allow you to splice your new wire in. (You may have to remove the regulator to make it easier, I know I did!) Put some electrical tape onto the old wire end, and tuck it into the harnessing. You need to splice your new wire into the wire which goes TO the regulator connector pin marked 'S'. So, when you are done, you should have a new wire that leads from your alternator (RED) to your regulator connector 'S' pin. This new wire should ONLY go to those two points. Now, using a meter, check for the following continuity: The heavy (YELLOW) wire from the alternator should have continuity to the RED BATTERY cable. On the alternator connector, check for the following continuity: The RED wire should have continuity to the 'S' pin on the regulator connector. The other wire (ORANGE/LT BLU) whould have continuity to the 'F' pin on the regulator connector. If all checks OK, re-install the regulator (make sure to tighten the bolts properly to the chassis, grounding of this part is important), reinstall the battery, start the car, check to see if your 'BATT' light goes out, if so, check voltage across battery while car is running, hopefully now at least 13.8, and, if you had the same problem I had, you're done! Good luck all! PS, I'm a non-Ford fan, especially after this nonsense!