charging issue please help

my truck wouldnt start one day so i jumped it and went to work. then the next morning it happened again. so i went to see if my my alternator was bad and he tested the battery first and it read 4.6 volts. so i got a new battery but then got drained to 6.6 volts. then i put the new alternator on
and i was told that doing that fries the alt which it did. so then i charged the battery up to 12.6 volt and a hand held trickle charger my dad uses to charge are trailer battery.

then i put another new alt and it fried that one. so i went out and got a brand new battery and a brand new alt and started the truck and it only read 12volts still. i checked all the fuses there's no draw there. i cleaned the engine block ground for the battery and cleaned it. the only thing i havent done is a voltage drop check. and that would mean that the alternator's wiring is messed up right?

i also bought an external voltage regulator. people on here said its my PCM because there's a a built in voltage regulator in it. so installing an external regulator would bypass it. so i think im gonna do that tomorrow morning.

also i fixed a fusible link before all this happend. i pulled on all of them and none of them stretch can they pop but the rubber stiffen up again?

any info is greatly appreciated. thanks