VT commodore Alternator problems

[swifty_ano]

My battery light came on last week and my battery would not charge.
So we bought a second hand alternator and a brand new battery for it.
The new alternator worked fine for 10 minutes. The battery light vanished but after 10 minutes it intermittently came on.
Randomly came on. After 45 minutes of driving I turned the vehicle off. After that it started fine but the battery light stays on.

I had a look at the new alternator and found that it didn't come with that little black box on the back (screws onto the frame and has a plug on a piece of wire that connects the the "+" terminal on the back)
I fitted the old box thingo onto the new alternator but no difference.

No I have checked all connections and all seem fine and clean. I used the inbuilt volt meter (special menu) and its reading at 11.8v at idle and drops down to 10.8v with lights on.

Now I dont have money to pay for a mechanic/auto electrician to look at the car nor can I afford to spend money guessing.
How do I tell whats actually wrong with it?

One would think that the fact it didnt come on until after a short while that the alternator is good? The connection on the back of the alternator seems clean and is not corroded (lug).
Any help would be much appreciated.

Anthony

[lout]

alternator is faulty or wiring not installed correctly

[MR_VX]

voltage regulator is stuffed (the little black box thing that bolts to the back of the alternator)
I wasnt aware that you could replace them, I thought you had to buy a hole new alternator? thats what i did anyway and its alll good now

[Catchy]

If the battery light is coming on intermittently, double check your battery and battery terminals are secure.. sounds silly but it happens.

[wrx884]

sounds like the regulator, would b cheaper 2 replace than buying another alternator. and hallf the time thats all it is. the 2nd hand alternator u bought could have simply had the same problem.