weird charging issue

My truck came with an externally regulated alt. The previous owner swapped in and internally regulated alt and hooked up the red wire from the connector. And I swapped higher amp ( his 25 amp mine 55 amp Toyota reman) alt made for the 22r. It had two connectors I hooked them up and everything worked fine most of the time. I taped the second to the yellow wire and it sender voltage and runs great.



But sometimes,getting more common, the truck will not charge till u rev it to about 3k then from the pass side can hear a relay ping and the volt meter jumps to 14 and it is charging. And clue why it is doing that( how to fix)? And what exactly is over there to make that noise ?



81 long bed 4x4 dlx