Altenator, battery issue or..?

[dkurganskis]

Hi, first of all I want to say that I am not a mechanic. I have purchased a 1990 1.8 scirocco scala back in October. The main issue with it was that it wouldn’t hold charge, meaning as soon as it was disconnected from jump leads it would just die.
I have replaced the battery and it ran until the battery fully drained, then same thing happened. So I thought if it’s not the battery it might be the alternator, so I found the correct alternator, fitted it all with the same tension on the belt. And
BINGO! The battery light on the dash was away and it ran for a good 5 minutes on its own, then suddenly it cut off again and back to square 1.
I have checked all the connections and wires and they seem to be ok.
The radiator fan doesn’t spin (probably needs replaced as it touches the outer casing), but I wouldn’t imagine that’s what’s causing it.
Any idea what the issue could be?

[GT_II]

First of all you need to fully charge the battery. Then, once you have started the car, measure the voltage across the battery terminals with the engine runnning - this should be at least 14v. If not, you have either bad wiring, a bad alternator or a major current drain from a fault elsewhere in the electrics. I guess the seized rad fan could potentially be shorting out, so unplug the wiring connector to the fan just in case.