check gauge light came on and alt gauge showed nothing was at zero. pulle din to a parking lot to check if it was anything else, truck was still running so with out thinking thought it was bad battery, well truck staled out. took off the alt and took it to auto parts store to have it checked, well it checked out good???? my thoughts here are if the alt is good then battery is bad then truck would stay running till i turned it off? confused is there any other electrical involved in that that would cause this? any help would be great and thank you

 

Typically, yes, I would agree. Since your alt tested good, I would start by having the battery tested at the parts store, and then checking/cleaning/tightening your battery cables and grounds. Another possibility is a bad regulator.