Bad battery drain, cant figure out where?

Ok, well we recently had the alternator fail on our '90 ford tempo, mechanic took out the old one, wanted an insane amount for a new one and to put it in, after haggling he got the old one refurbished and gave it back to us, i reinstalled it myself (just to be sure there are only two wires that needed to be connected correct?) when i started the car it ran fine, but the battery light was on, and it had never been on before. while driving it, it goes away when i get on the brakes. parked the car, and dead battery the next day. Got a new battery, and it was the same thing the next day. I broke out my multimeter and checked the battery after charging it and it was fine, i checked it running and its showing 18 volts...that seems really way too high to me, but i dont really know much about the whole charging system. I checked against my own car to make sure my multimeter is fine, and it shows about 14.5 volts on my car when its running. when i unhooked the negative cable to check for parasitic drain its showing a drain of 0.15 mA. I pulled all the fuses underneath the drives side dash and nothing changed. I unhooked the alternator and no change. Can anyone point me in the direction of what i can check next or what may be the problem?