Hello Al,
Where did you get the alternator from?
Thanks,
This is a very straight forward charging system. The whole works are integrated into the alternator, and i'm sure you just happened to get a bad one. The internal voltage regulator is malfunctioning.
You will need to take the truck to them and show them and they can test it right there on the truck. The reason i say to take the truck there instead of just the alternator, is because alot of times when they bench test it, it will show its good, thats because this can go intermittant. So its important they see it.
Replace it, and i'm certain it will fix the issue.
.
If you have further questions on this, please feel free to reply.
Master Tech
30 years/Master Tech. Foreign and Domestic
Oops, missed that one..
If the fuse is good then yes, most likely its the switch, VERY common to fail.
You can verify it by jumpering the orang and white wire at the switch,,if they come on,,,replace the switch.