Help with 87 4runner charge light keeps coming on!

Hi i have a 87 4runner and last week i was driveing it then the Charge light and brake light both come on so i took it to advance auto they tested it fine so i drove it awhile after that then it started smoking under the hood and smelt like burnt wries so i got it home and pulled the hot wire off the bat while it was running and it died so i went and bought a used altanator which i was sure was the problem cause the old one smelt burnt up so i got the other one on and it worked fine then the next day the dam lights come on again and they come and go and what i notice when they come on the volts meter shoots up to 18 volts then when the lights go off its back down to 14 so is this mean i have a bad volt regaltor or something in the wireing? cause i know 2 altanators doing the same thing is highly unlikely.

any ideas?