burning up voltage regulators

have replaced both voltage regulators and stator on 96 merc. 150 efi. All was good for three outings,now one of the new regulators is already burned out again. It was the one the tach. is hooked to,but it worked fine until the voltage reg went out. Any ideas on other things to check out would be a big help. Battery reads 12.5 volts and ran acc. and cranked over motor fine. The electric choke on my key switch is not working,and fuel guage not working either. Not sure if a "short" in these could burn up regs,or if it would just take out a fuse. Thanks for any help!