1984 ford E350 chassis van terra turtle top motorhome

I just purchased this motorhome and discovered the needle on the amp gauge sweeps violently back and forth from charge to discharge. The lights surge as well. I have replaced the alternator and the voltage regulator and the battery to no avail. I also checked the wires coming from the alternator and voltage regulator any help would be appreciated thanks. First time User and motorhome owner.