HEEEEEEELP! I have an 87 Tbird LX with 5.0 litre EFI the instrument cluster is digital. First car wouldn't start battery dead. Replaced battery. Battery run down again. Replaced pos and neg leads and new acdelco alternator and also installed the new 3 wire connector/harness that came with alternator. Everything now seems ok charging at around 14.8 volts according to multimeter. 2 days later battery icon flashing in instrument cluster indicates low charge.I took alternator back to supplier and installed replacement. Same thing. I noticed a small squarish black plastic piece in the wiring harness BEFORE the area where I spliced in the new 3 pole connector body that came with the first new alternator it does not appear to be openable, would this be a fusable link? Without unwraping all the insulation on this harness it looks like the 2 heavy guage wires from the connector transition into one single conductor. Anyway this is driving me nuts and as I live paycheck to paycheck I can't afford to take it to a diagnostic expert. ANY responses, ideas and tips/info would be greatly appreciated. 8)
What you can do is just check for a bad alternator by simply starting the car and once it's started take the positive cable off the battery. This will turn off the car if the alternator is bad. If not then it's not the alternator. Then it would be an electrical problem. Eventhough they exchange your alternator it doesn't mean it's a good one. I had to exchange an MSD Ignition Box 3 times before I got a working one.
Checking for an electrical problem is simple too. If the car turns off. Put the key in the off position and connect the positive wire back to the battery terminal. Now you gotta do this in a quiet and preferably in a somewhat shaded area, Ok when you place the cable back there should be a click or you should see a spark, That means that there is a short or that a switch that is on. Check all the switches and make sure they are off, High beams, sunroof, just miscellaneous switches should be checked to see if they are off and then retest the connection.
If this problem persist, then it should be checked by an electrician. My electric guy charges 60 bucks to tell you what the problem is and fix it. Just make a couple of phone calls to local automotive electricians.