1994 Dodge Caravan voltage is high after recent altenator r

My 1994 van was needing to get jumped quite a few times so I replaced the altenator with a rebuilt 90 amp altenator. After driving about 160 miles I noticed one day while leaving a parking lot that the 'check engine' & 'check gauges' lights were on also the voltage meter was pegged at 18 volts. When I looked under the hood the belt appeared to be fine. When I got back in the van and revved engine the voltage meter fluctuated, then went to 8 volts and the engine died. Assuming that the altenator was the culprit, I had some one help me get it started( I don't know exactly how, he said he did some proceedure to trick the brain). I also discovered that a 15A fuse in the fuse panel under the hood marked engine control was blown, so I replaced it.
When it started again the voltage read 18volts again. So he used a altenator tester that said the amperage varied from 0 - 70 amps and the voltage varied from 15 -18+ volts.
So I replaced the altenator with a replacement from the same store, telling him that I had been given a faulty unit. After reinstalling the altenator, and re-replacing the fuse, it went to 18 volts again, so I don't THINK that this altenator is bad. I've looked for a voltage regulator in my car repair manual but I have'nt found one. Please help me get this van running again. Thank You!