1991 Spirit R/T volt meter fluctuating

I noticed the needle of my volt meter bouncing around a bit, and I got a code 46, which says the system is overcharging. I assumed bad voltage regulator, and I assumed it was built into the alternator. Well I put a new alternator in but I'm getting the same fluctuation on the volt meter. Any ideas?

For some reason Dodge built the regulator into the ECU, so you either replace the ECU or install an after market regulator (much cheaper). I did that to a friend of mine's Durango, and the battery never died afterwards.