Battery light

Electrical problem
1998 Mitsubishi Eclipse 4 cyl Front Wheel Drive Automatic

Ok. So I have a 98 Mitsu Eclipse RS with a 2.0 420a in it. I've swapped out the alternator and made sure I correctly repaired the 2 prong wiring harness that connects it to the ECU. My battery light still comes on after about 15 seconds after the car is on. What in the world could be wron here? It is a remanufactured alternator that was bought and tested from autozone before installation. Could this light be coming on because my battery was at around 11.5 volts and than what should go in the car? Please I desperatly need some help here. Especially before I say screw it and take it to the dealership and pay out the rear to have this fixed.

I have one more idea. One would be to trace the 2 wires that connect the alternator to the ecu and see if they have a break in them. And 2 I've got the alternator belt pretty tight as is. The crankshaft pully looks perfectly fine. No weeble wobble of any sorts. After all is said and done I fear that my only next steps would be to order a new ecu and if that doesn't work take the damn thing to the dealership. Just don't understand it. I have just about replaced the entire charging system, wires and all, outside of the ecu and the 2 wires connecting it. You don't supppose there's a fuse I'm not seeing outside of the one under the hood?

After a recent repair, cv half shaft replacement, lower ball joint, and new battery terminals, the car battery light was on. After dring a few miles the car head lights, gauge lights dimmes, and enginee sputered and quit slowely as did power steering. The car enginee will start when it is jumped but will soon die a slow death. I belive the problem is the alternator. The polarity on the battery terminals was briefly switched buy the villege idiot and smoke came from the ignition and the car would not start. Then this major problem occured when the polarity was set in the correct positon. PLEASE HELP I AM STUCK IN THE MIDDLE OF NO WHERE AND THIS CAR IS THE ONLY WAY I HAVE TO GET TO WORK. What should I fix and how should I do it to make this P.O.S run again.

I will check the fuses with a multimeter. I did a visual inspection and none appeared blown, I will test with a meter. I checked the voltage on the battery it was low it was around 4 volts instead of the normal 12 volts, it is a new battery, so the polarity switch drained it when the damage occured. Also I did some reading on alternators and it appears` that they generate power, the car will run brifely when it is jumped but will quickly die. Also when the polarity was switched in the wrong position there was excesive sparking on the battery leads, small ammounts of smoke came from the ignition where the key goes, and it would not start. When it was switched to the correct polarity it started perfectly and ran for a bit then the lights dimmed the enginee sputtered and it died, and would no longer start unless jumped, but as I said it quickly dies.

I finaly got the alternator replaced. The voltage drop on the battery has stoped. There are a few new concerns though, the car starts the first time I turn the key runs ok but sounds as if it has way more power then before, also the needle moves up and down slightly. And the battery light comes on when the car reaches normal operating temprature. Also the heater and defrost doesn't work. Where should I start to fix these problems. I checked the fuses there were 4 small fuses blown 2 10's and 2 15 fuses. I will replace them, could they be causing the heat to not come on and the battery light to stay on.