amp light issue

ive got an 88 vert and i just installed a one wire 200amp 3g. i ran 4awg from the out on the alt to the selonoid. the entire stock herness for the alt is not connected to anything. while the car charges fine the problem is when i turn the key off the amp idiot light comes on on the dash.v soon as i turn the key to on or start the car it goes out. i tried connecting the green wire from the harness #904 to the green wire that comes out of the d plud on the alt (which came clipped off at the4 connector) and it didn't change anything. has anyone had a simulkar prob or can anyone tell me exactly what causes the dash light to come on? from what i can see with 904 green wire disconected there shoulkdnt be any way the light woulkd come on.

thanks guys

found the problem the factory splice on the original output wires had cut into and was shorting out to the green wire in the harness.
i know 4 gauge is snall but i got a deal on the 200 amp unit and had previously ran the 4ga for a 130 amp unit. as i cant foresee ever pulling 200 amps i simply put a 130 amp fuse at the alternator output so the will blow before the wire ever gets over loaded. ill upgrade it in the future. thanks for the heads up though