Bought a new alternator today and put it on wasnt able to crank the truck .. Put battery charger on it and was able to get enough to start it but it wouldnt hold. Volts keeps bouncing till it dies checked fuses and battery .. I just need some idea of what it might be or where to possible start looking I'm getting flustered

 

Well,,,, If the battery won't crank the engine, or if it barley does, it needs charged. Besides the belt on, cable hooked up, you say the voltage bounces till it dies. With what you posted, I'd suggest cleaning the battery connections, and revisit them

 

Check the mega fuse to see if it's blown and clean the contacts where it's attached. Make sure grounds are making good contact.