1992 regal voltage problems

hello everyone, my problem is almost everytime i hit my brakes, my volts go down under 13, also at idle it does the same thing, any help is appreciated, thanks.

your alt more than likely just has dust or crud inside. is it original? it is not uncommon for this to happen. 13 volts at idle is ok. what made you check voltage?

voltage measurement in the dash, at idle it will be at around 14 volts then all of a sudden drop below 13 sometimes near 10 volts and everything will dim, then it will go back up to about 14. alternator is not original