Am trying to help a friend. He has a 1990 ocean Alexander with twin cats...3208s. On the lower station control planet there are two idiot lights one port and one starboard. The markings on the lites are ALT LTS. The issue is the port lite activates when the engine starts. The alternator is charging the battery at 13.5 volts with battery charger off. Is there anything other than an alternator attached to this lite. Is this light activated by a going to ground. On my motor coach I had an alternator light which would activate and the voltmeter indicated proper charging. Turned out to be a broken ground wire. Should I start chasing the ground?