Any ideas about lack of charging?

I have a 1991 Mercury Capri with charging problems. Heres the story. I bought the Capri for 800.00 and everything was great. Then the alternator started messing up. It would charge and then it would stop for awhile then start again. It would got out and then come back on after about 10 or 20 miles of driving. That went on for about 2 months. Then one night it quit charging and never started again. I was stranded and needed help. I got so mad at it i put a hole in the top of the battery with a wrench i was using to try to coax the alt to start again with. A couple of days later i found another 1991 capri that didnt run but had all the parts there. So i bought it to use as a parts car. The first thing i did was take the new soft top and put it on my car. Then came the alternator. I pulled out the one from the parts car to put it in the other car. That was a pain all by itself. So the alt was working good for about a week or so then i noticed that every once in while it would overcharge then under charge then be ok then start messing up all over again. That went on for about 1 month. One day i was on my way to pick some parts for my wifes car when the alt decided to quit charging all together. Stranded once again. At that point it was time to fork out the 170.00 for a rebuilt one from checker. Thats the third alt in 3 months. Alas, charging!!!........ For about 2 weeks. Then guess what? You got it no charging. Only this time the battery idiot light never came on. Again stranded. Thank heavens i bought an alt with a lifetime warranty. I figured maybe i just got a bad one from checker so i took it back and got my second new one and fourth all together. This time i didn't get a chance to get stranded because right off the bat it was not charging. By now i'm pulling my hair out. I went to checker and they told me they can't check this alt on thier new alt. checking machine because the machine was lacking the proper lead. So they checked it while on the vehicle and told me they could not detect a charge from the alt. DUH! I had them order me yet another one because i've depleated there stock. While i was waitng for the next one i removed the wiring harness and inspected each wire individually from one end to the other. Everything looked fine. The next day i put in the third new alt. Still nothing. I expected it this time. What now?? This time i decided to go to autozone and see what they thought. They could not check the alt on thier machine either but they did have a very cool portable machine that they wheeled out to my car. Guess what it said? No charge detected. Yawn!! They also told me that my battery would not work when put under a load test. So i bought a new expensive battery from them thinking that it would take care of the problem. They suggested that i get my money back from checker and try a different brand alt from them. So i did. My fourth new one! The day i picked up the new alt from autozone i noticed that it was the same damn model (bosch) as checker had. But it was in a duralast box. I guess that makes it different. Anyway, off to home i go to put in this one. Great, its in. And i've got a new battery all is well. Yeah right! Same thing. no charge. By now i'm going nuts. not knowing what to do next. So i called the ford dealership and they told me for $95.00 they can pinpiont the problem and give me an estimate on how much to fix it. Ok lets do it although i'm not happy about it. Two days later they call me and say that they really cant tell what the problem is but what they suggest is that i go with a brand new factory alternator cause I must of got four newly rebuilt bad ones. Really? I said, How much will that be? when he told me i fell over. They wanted $525.00 wholly cow thats robbery. Of course i said NO! Heres your $95.00 and thanks for nothing. I just got back from autozone with my fifth new alt. And guess what? still no charge. I've took my steering column apart and changed the ignition switch. I've looked at and recovered the wire bundle. I've gone through all the fuses. I'm ready to jump off a cliff. I'm very sorry for the long long version. I guess i wanted you to be able to feel my pain. If ANY one has ANY idea about this and it works i will by you dinner. Thank you very much for your time

Hello,
I have just bought a 1991 Mercury Capri XR2 and I have to change the alternator. Did you ever figure out what was the problem with your car?
Thanks
Guy

Does this car have an external voltage regulator if it does check this. When you pull this item sand the plate it mounts on good and reinstall it this is a major cause of no charge or intermittent charge.