Can't get my guages to work #&#%!

I'm just finishing up my car and I can't get my guages to work. I've got 12 volts coming in to the constant voltage regulator but can't get a steady 5 volts coming out. All the guages check out good and I put all new sending units in. This is for a rally dash in my 1970 Duster. If anyone has experienced this problem or has an answer please help. I know Fords had this problem and they make a separate module to fix the problem. Any help is greatly appreciated. Thanks.