How do you find starter relay?

I have a 75 e15 iveco and have problems with starting ,
Started of with no batt light , replaced ,alternator now starter is over running on start up , and sometimes it starts on just turning key once to normally ignition lights on position ,and starter will go and keep going until you rev it up and batt light goes out , is it a starter relay prob , and if it is where is it exactlly as I am a novice on DIY repairs and have tried to get a manual for repair