I have tried 2 remanufactured alternators & there not charging what would cause them to not charge?

Thanks for the reply asemaster 6371 ! There's only a gauge no light. I tested the heavy red wire with a test light & there's power, I tested the connector wire and it has power with the key on. Tested the battery with dvom & it reads 12.58 with the van off & it read 13.89 w/van running. Sometime when I turn the van off & restart the charging voltage will read 13.01 & start dropping down into low 12's

If im not mistaking its a delco reman. Im not absolutely sure, I purchased it from a local parts house. I dont know if they do in house rebuilding but it has a warranty. I really would like to try another rebuilder, this is the second alt. From these guys, ill replace it today & see if the problem go away! Thanks again asemaster6371 ill let u know the outcome !