Electrical issue

While the car in question is not a professional car, I am awed by the knowledge on this board so I thought I would give my problem a try. I own a 2006 Lincoln Town Car with approximate 167000 miles. Less than a year ago, the battery light came on. I immediately took it to my mechanic who diagnosed a bad alternator. With said alternator replaced, I felt I was free and clear. Not so fast. Within a couple of months, the battery light would illuminate but only for a minute or so and with no known pattern. Once, when on, I happened to be within yards of my mechanic, so I stopped by to have him check it out. While waiting on him to get his test equipment out, the light went out. However, in the process, my car overheated due to the fan motor failing. I suspected maybe that a failing fan motor was pulling too much thus causing the battery light to come on. With a new fan motor, I was on my way. Then, within weeks, the battery light came on again. Same pattern insomuch at that it would only stay illuminated for about 60-90 seconds. Shortly after that, I was greeted with a dead battery. With the car back at the mechanic, he assured me the alternator was functioning like it should and within the set limits and sold me a new battery. He also took the time to re-set the computer. Within a few weeks, we were back to the brief battery light. He said that he would do some checking around and thought perhaps a wiring harness had gone bad. In the mean time, the air ride compressor died. So, when I took the car in to have it replaced, my mechanic replaced the wiring harness. Hoping beyond hope that perhaps the air compressor was pulling too much thus causing the battery light to illuminate, I felt that the end of the mysterious battery light was near. But, it was not meant to be. The battery light has illuminated twice within five days of coming out of the garage. The only thing I have not done is take the car to a Lincoln dealership to have them run a diagnostic scan. Having done some internet research, I have read on a couple of message boards that some Town Car, Grand Marquis and Crown Victorias will do exactly what my car is doing and there is no harm and also no solution. So, any suggestions at this point would be greatly appreciated!

it sounds to me like a diode in the alternator is sticking or going bad.

My 2006 long door town car as of now (we do not use it from December to April) has 443000 miles and is going strong. It qualifies for a pro car Carey had some interesting mods done. That said your issue is a typical glitch encountered with this series of cars,one of my Crown Vics is currently throwing a door open light on when the spirit moves it. Throwing parts at these cars is not how you repair them you must find the problem. Sometimes a corroded connection a pinched wire many of the cooling fan assemblies have been replaced (big bucks) when the issue was not the assembly but the control module or the plug corroded with salt. We had a no start issue with the town car two years ago (would not turn over) after much thrashing about it turned out it was a diaode located in the right front fender fuse box corrosion had lowered the voltage and the diaode expired from low operating voltage cleaned the fuse box with electrical contact cleaner replaced diaode no more issues. AS far as rebuilt alternators go watch what you buy DO NOT buy any rebuilt that does not carry a lifetime guarantee the quality of rebuilds varies greatly and if no warranty NO SALE is my motto. We had one local municipality went low bidder on rebuilds for the cop cars at one point 1/4 of the fleet was down with alternator failures.I still use a local old timer who does them in his Shop his getting ready to quit though.

the shot gun approach is what most shops are stuck with as the time to trace repair and clean a connection for a intermittent problem can be a all day event.
with no guarantee of success. but to charge a poor soul 50 to 100 bucks a hr for all day and still not fix the problem is a sure way to have you business go down the road. but as peter said 9 time out of 10 it's a bad connection. the best tune up one can do is putt the plugs apart in the harness and clean then and use a little dialectic grease put them back together.

of course you risk the broken plug and pulled apart wire if you do