To make this simple get a manual.
I will assume(But not sure) the alternator is a IR(internal regualated type alternator). THat means its on the inside.
The early Luv will have a external regualtor. close to fender next the alternator
You could take it to autopart store and they can test this for you to say if its good or bad.
Those lights.
Make sure you dont put some High power lights in there that should run off a relay instead of using the stock wiring. Could melt wires but should blow the fuse first.
If say 80/100watt light on place of the stock that could be the proplem so put the stock back in. Maybe look up a 4x4 site that can show this or look up a Hella
sitehttp://www.rallylights.com/hella/headlamps.htm
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