no this is definetly not recommended. the alternator puts out rectified a/c voltage. the battery then filters the ripples out of the waveform to make dc voltage.

this testing method worked good on your grandfather's 1950's edsel that had a low output generator. but is not something you want to use on any car manufactured in the past 40 years that has an alternator.

if your alternator was actually working, you're likely to burnout the regulator in it from the a/c voltage spikes. and then toast various expensive electronic modules around your car and maybe even deploy the srs airbags too.

Today I'll remove the battery and take it to be tested at a couple of local auto parts stores (Autozone, Advance). Not really sure what else to try at this point...

Try this:

Thanks, but my battery terminals are in pretty good shape, and voltage on the clamps is the same as the terminals themselves.

So anyways, I figured out at least one thing that was wrong: My multimeter's own internal battery has been dead/dying this entire time, and has been giving me bogus readings all along. I knew something was wrong when I tested a 9-volt battery and it was relling me 11.5 volts....and then the LCD screen flickered and died. I'm sure somewhere, this is really funny.

So I put a new battery in the voltmeter and retested everything. The car battery is strong at 12.5V with the engine off. With the engine on, I am reading 11V with both the original and junkyard alternators, so clearly neither one of those is charging. The battery light on the instrument cluster does not function at all with the junkyard alternator for some reason, but stays lit full-time with the original. The cluster voltage gauge also reads consistently low with either alternator.

So I guess a NEW alternator is what I need. And next time, I'll pay more attention to the batteries in my own tools.

New alternator has been installed (Duralast from Autozone), and the first engine startup saw an immediate improvement as the battery light stayed off and the voltage gauge took its usual place in the middle. Voltages were 12.5V engine-off, and 14.1V engine-on. I took her out for a drive.

Everything was peachy until I tested how it reacted under a WOT acceleration. At that moment the battery light lit up yet again and has stayed on since. The voltage gauge has not moved. Got the car back home and tested voltages, and I'm now getting 13.6V engine-on. Engine-off is still 12.5V.

So what is it now? Did I get a power drop-off and it'll take the engine some time to recover it, or what?

no "time to recover" is required.

the alternator warning light on the instrument cluster in these cars is controlled by the alternator regulator. when you first turn your car on, +12V flows from the ignition switch through the lightbulb to the alternator regulator. the regulator provides a small amount of power to the field coil windings to create a small amount of magnetism in the alternator field coils. once the alternator is spinning at a reasonable speed, it begins to create electrical power inside which then applies +12V to the charge light line. a bulb will not light if it has +12V present on both terminals because their is a 0V potential difference between the two sides.

have you replaced your battery lately? these are usually only good for a couple years before they begin to sulfate significantly inside. and with your overvoltage adventures, the battery is probably low on electrolyte inside as well.

also, did you look at the battery grounding system? i'm suspecting the big one near the starter must be good if you're able to crank your engine over, but there are two others. one connects to the fender right beside the battery. the other is a braided strap towards the back of the engine bay and connects the engine to the firewall.

the battery cables don't only corrode on the visible exterior surfaces, they corrode internally underneath the protective plastic wiring jacket too. for an idea of how corroded the wiring is inside, you might try measuring the voltage drop across it while the car is running with lots of high draw electrical accessories turned on.

The fender ground next ot the battery is good, but I'll admit I cannot see the other one at the back of the engine. I can follow the cable some, but not all the way to the end.

I'll admit I have no idea how old the battery is. I just went out and started the car after letting it sit for the last hour; initially the battery light was off, but the moment I gave the engine a little gas it lit right back up and stayed on. Voltage before the rev was about 13.8...after the rev 13.6.

I turned on the headlights, A/C (for the cooling fan), and all interior lights and checked the voltage again, and it stayed solidly at 13.6V. I am seeing an intermittent 0.1V drop from the alternator to the battery, I.E. the battery reads 13.6 but the alternator itself 13.7.

I suspect some combination of new battery and/or new battery cables will fix whatever is going on here.

I checked the electrolyte level, and it's full and clear-looking. I should point out that the supposed overvoltages I was reading were taken before I realized my multimeter's own battery was nearly dead and skewing all the numbers. I'm not sure I was ever actually over voltage. I suppose it's still possible the battery is weak, but you couldn't tell by looking into the internal vent holes.

Can a car battery reach a point where it refuses to permit the alternator to charge it up to 14-14.5V? I'm trying to understand why giving the engine a little gas makes the system voltage drop enough to light up the battery light.

Sounds like a wiring problem. Have you removed, cleaned, & tightened the battery terminals? Have you checked the OTHER ends of the heavy battery wires?

If the battery was preventing a good alternator from reaching 14V (drawing too much current), the battery would get so hot it would probably explode in a minute or 2. But bad wiring (high resistance; not enough current) can cause your symptoms.

here is a picture of the braided engine ground strap on a 00' crownvic that connects the engine block to the firewall. it's somewhat buried underneath other components, so you can only see the top portion that attaches to the firewall tab in these pictures.

the engine bay, pay attention to the left rear portion near the heater core hoses and evaporative emissions valve



a closeup of the area near the heater core hoses & evaporative emissions valve showing how the ground strap lug attaches to the body of the car.



this component is often broken during engine swaps because mechanics remove the engine with the strap attached to it but forget to remove the retaining bolt for the strap from the firewall first.

here's how the battery cable ground is supposed to bolt to the fender in a 00' crownvic. there is also another ground terminal underneath this one for the airbag system.

Okay, I removed the battery and took a metal brush to each post and terminal clamp, cleaning them off until there was nothing but shiny metal on all. Checked the grounds next to the battery and they were good; voltage checks at these grounds matched up perfectly with the battery voltage.

It got too dark before I could locate the rear firewall grounds; I'll try to locate those tomorrow. After the battery cleaning I reinstalled it and started the engine; voltage looked good at 14.1V. Revved the engine some and the voltage still held steady, no battery light. Will test more tomorrow.

here's a picture of a 00' crownvic engine removed from the car showing the other end of the braided ground strap:



normally, there would also be an egr dpfe sensor mounted on the bracket that the ground strap connection is connected to.