Alternator wont charge

. I started it and the battery light stayed on. The voltage gauge showed only battery voltage, (11-12 volts). I took the alternator to the parts store and it passed the test twice. I placed it back on the vehicle and it still would not charge. I purchased a new one and put it on. It still wont charge. It is a 1 wire type. Through research on the internet I think that there is a short between the alternator and the battery light on the single wire. Does that sound plausible? If so how should I wire a replacement wire.

Thanks for your help,

Robin