electical problem

my 94toyoto corrola,warning lite came on( referred to manual), and it said "take to toyota dealer--electrical problem- I'm not close to a daler so I took it to a mechanic, he put a new alternator in it and said it was overcharging. Now a week later, the lite came back on. IS the only way I am going to find out what the problem is , is to take it to a toyota dealer?

this warning lite....is it the check engine light (symbol of an engine)....need more info on what kinda 'warning lite' this is.