Mitsubishi: Expo Alternator

hello guys,

My friend has a 92 expo with 4 cyclinder. He has some problems with his
alternator. The battery dies after some use. I thought it is alternator
since the symtoms. We changed the alternator, but it is doign the same
thing. He does not get 13 volt+ when the car runs onbattery therminals.
I'm thinking there is a break in the circuit between battery and
alternator. Do you have any suggestion where to start.

TIA

Thanks.