problems with electrical system..not alternator or battery

how do you know its not the battery or alternator? Also under drive pullies cause poor charging at low rpms. I would check the main ground wire running from your battery ground to your block, then check the ground wire on the back on the heads to the firewall. If that checks out good then get a battery tester that has a load tester on it and check your alternator and battery for correct voltage under a load.

Get Grounded

I think you're on the right track. It sounds like a ground problem. I don't remember, is the voltage regulator part of the alternator. If not, check that out. My manuals are at home, or I'd check it out for you.

When the RPMs die down, are you sure it's not an idle problem. If the engine speed decreases, you'll also get the symptoms you stated, except that the fuel pump should not slow down since the battery should be able to sustain it.

Does it condition happen when there is moisture in the air? If so, you might have a wire with broken insulation touching the frame, i.e. a short somewhere.

Check your battery ground wire and leads from/to your alternator. Just guessing, the problem is going to be a major player in your electrical system, i.e. alternator, voltage regulator, or battery.

What was the last modification you did? Check the area around where you worked. I’ve done it. While working on one thing, I broke another.

Good Luck,
p51302

if there are bare wires that have power running through them next to metal then it could ground out against it and cause the car to short out and want to stall. I know this from personal experience because I had a wire melt on me on my msd ignition and when the wire would touch the metal body it would short out and my volt meter would drop and the car would almost stall out. I would not recommend leaving bare wires anywhere that have power connected. Just follow the main ground wire on the battery down to the block, its on the drivers side near the oil pressure sending unit by the waterpump. If that wire if frayed in anyway it will cause hard starts and poor charging. I know because I just replaced mine and it was causing this and it was frayed on the end of the wire by the block.

It could be your coil....that controls your spark, which controls the motor, which controls the alternator. If the coil is failing, you'll loose RPMs and then your alt. won't charge. Also, it could be your igntion switch where you put your key. Ford had a recall on them back in the day, and if yours is shorting out, it might cause problems. Last thing to check would be for bogus grounds, because that'll do it too. I just wanted to give you a few ideas.

Are you talking about the 3 wire plug, they are famous for melting and starting fires. Replace the plug (available at most part stores) or I'd upgrade to a 3G it is a good upgrade.

I also replaced my wires (got them from parts america, aka Advance/Checker) for under 15 bucks, if I remember correct (it's been a few months) My problem like yours would happen when I was turning, my car would stall out - that was caused by 2 things, one I had a loose wire for my interior gauges that was grounding out (you can imagine how long it took to find that one wire... the other was the starter switch, which, when I would turn, would make the car turn to "accessory" mode, stalling the car...
If you haven't replaced the starter switch, it's worth doing anyway, it's under 10 bucks and takes less than 15 minutes to switch... (Plus it's one more new part on the 'stang!)

I know problems like this can be frustrating. Just keep plugging away at it. You’ll get it.

Fix your known problems, the alternator wires. Then see if the problem still occurs.

Again, your analysis is correct. Your alarm will kick in if the voltage drops too low. It definitely appears to be a grounding problem. Just like everyone above having the same issues; something in your car is grounding out. Fix the alternator connector and then inspect around areas where wire insulation could have been damaged, i.e. by the battery and areas with a great deal of heat.

I suggest the following. Carry a voltmeter in your car. The next time your car doesn’t start, have someone or you apply the voltmeter across your battery to measure the DC voltage. Start the car. From memory, it shouldn’t drop below 10 volts or so. To determine what the normal voltage is, perform this test when the car starts right off. If the voltage drops excessively, it does have enough amps (power) to turn over your car. This condition could be caused by a bad battery, bad alternator, a short, or something like this.

From the information you’ve shared so far, it appears that the alternator is not fully charging the battery or shorting it. Since you were trying to start the car, the battery is doing all the work. It has to have enough amps to turn your starter. But, it couldn’t. It could be because your battery didn’t have enough amps in it to turn over your motor or the battery was being shorted out, somewhere, not allowing it to provide enough current to the starter.

I’m sure I don’t have to say this, but this is a serious condition since a battery could explode if it’s being shorted out.

One last question, how long have you had your underdrive pulleys installed?

Good luck,
p51302

based on the alarm observations, i agree with others about the lack of grounding and pos cable flow. remember, you can have a good 5 million amp alternator, but if you have a bad cable or a bad battery (dead cell, etc), all is lost (not literally).

the cables can rot from the inside out. also, take them all off and clean them, even if they look good. i have had to do this on some of the crotchrockets i have. on stangs it is important since the gauge of cables used is kinda marginal. add a little rot or resistance, and it is sub-par.
as cables heat up, they become less efficient. and since your problem is intermittant....(not saying that what i have said is the solution or all of the answers - i did not read all of the thread)...but i would check this out (again). also, running another motor to frame ground is a good idea (and critical if a higher output alternator is used).

just my two cents worth. good luck.

As previously mentioned the stock alt gauge is in the charging circuit, finding a grounding problem in the charging circuit is a real PIA, and very time consuming.

Earlier in this thread someone said that it could be your ignition harness. I would strongly suggest checking that out. they're just poorly made. I'm actually about to go out and buy one, since mine is zip tied together. Electrical is the worst to find. I'll put it in example in a simile. It's like a huge array of water pipes, where there's a series of checks, valves and seals, and to make it that much easier...all the pipes are 30 feet underground. And you have a leak that's disrupting your system. So what i mean is, your voltage problem can be a number of things. If you have the money, you could always take it to a shop. But expect to pay a pretty penny. Good luck, man...with your problem.