The battery light may illuminate on the instrument panel because the alternator wire harness connector is damaged. A new connector kit is available and should be installed to correct this concern.Google+
Car Problem Reports
Ford Ranger Battery Light Due to Damaged Alternator Wire Harness Connector
Ford Ranger Problem
Visitor, 1993 Ford Ranger, 126,831 mi
battery light is on gauge shows that everything is working as it should..
got out my volt meter and battery shows 12.8 with truck off and 14.78
with truck running at idle which is within specs for my 93 ranger with 2.3L...
after a little more research i found that the idiot light uses a
separate wire plugged in to the alternator,
on my 93 this is a white wire with black stripe and from what i have read
the connector within the plug will corrode and break....
have not been able to repair yet as it is a pain in the back side to get to
but wanted to let everyone that finds this post know it is best to check your
alternator output first before spending the money to replace as it me not be
the alternator that is bad..