1995 Honda Civic overcharging! Help

My civic is overcharging, ihave put sevral batteries and have 2 aletrnators, I cant figure out what is causing the overcharging, normally it shoudl charge around13 but it is 18, 19 and sometimes 20 volts, I knwo that it is too high and could result in blowing many things such as fuses and bulbs, ive had both alternators in with all 3 diferent batteries, the batteries are good ive got them tested and have load tested them myself, I can.T quite figfure out if there is a regulator somewheres on the charging system or if its is just my luck with 2 bad alternators, any suggestions, if it results to be a ground or regulator, if you ahve a suggestion of a website with diagrams or if you would have one that would be great! To help me fiugure out my overcharging problem