Alternator stops charging once the engine warms up

[Kolusion]

I hosed down the engine in my 1991 Honda Prelude without covering the alternator and afterwards the battery charge light came on and would not go off, so I replaced the alternator with a remanufactured unit. That remanufactured alternator worked for half an hour and then never worked again so I replaced the remanufactured alternator with another remanufactured alternator. At first this one didn't work at all but then I degreased my oil soaked engine wire harness and afterwards it started working but only for anywhere between 10 minutes to 30 minutes from starting the engine cold. If I start the engine warm it will not work at all.

Cleaning the oil soaked engine wire harness made me think oil had gotten into the wires and caused problems but then I realised I have tested all the circuits at the alternator (IG, S, L, FR) and they are all at the voltage they should be. Also, I checked the alternator related fuses and alternator grounding which are fine, too.

I know the alternator turns off because there is no decrease in voltage on the FR circuit when I turn on the headlights and rear defroster when the battery charge light is on.

Does anyone have any ideas?