AE8616v

Hey guys its been a while since i posted on here but i got another first gen its an 84 gsl streetported 13b 4port, racingbeat intake holley650, racingbeat exhaust manifold, 3 inch exhaust to a flowmaster muffler. Ever since i could drive ive owned rotarys but never a ported one and it feels great the torque range is wayyy better then a stock motor and it just all around feels alot better. Now onto my problem i had a s5 alternator in it for a while and it would spike up sometimes and go to like 16 volts on my charging gauge which kinda made me worry so i took it off and put the stock one back in and now its doing the same thing. any ideads on why it would do that my guess would be somtehing grounding out that shouldnt be its seems like its worse when it rains and when the passenger door is open. oobtw i do have an dul electric fans so i think im gonna go back to the s5 alternator it idled alot better with it