The car is a 440 six pack '71 roadrunner. It has a stock charging system with 40 amp alternator. Typically the ammeter shows a slight discharge at idle, but lately it has been showing 3/4 charge at idle and with any increase in RPM it shows peak/max charge on the ammeter. I have checked the wiring, and replaced the voltage regulator and still no difference. I found some questionable connections at the firewall and they were fixed. I had the alternator tested at autozone, but I'm not sure they knew what they were doing. What should I do next? Any ideas or suggestions are appreciated

70 & up flat reg correct? Sounds like classic bad reg or reg not grounded. Assuming the new one is good & you grounded it to bare metal on the firewall then I'd take off the 2 field wires from the alt & take off the triangle plug from the reg & (1) jump 12V to either of the alt male field terminals and (2) 12V to the "top" male bullet terminal of the reg triangle with it facing up like a pyramid & (3) jump from the other alt male field terminal to the "side" reg male bullet terminal & see if it charges like it did before with the slight discharge at idle which is normal for our alts'. Might check that the eng is grounded well to the firewall with one of those metal braided straps but with the wiring jumped if it's still acting up then either the alt or the reg is bad (likely the reg). Holler how it goes. Need 2 double female "bullet" connectors to use on the reg bullet terminals

Have you checked the battery voltage when it shows alot of charge ? Sounds like its overcharging. If its the electronic reg do as was said and make sure it has a good ground but also make sure the blue (12 volt) wire has a good connection. I have seen that connection bad and then the reg does not know what battery volts is and will keep charging thinking battery volts is low. With the electronic reg anything that is grounding the green wire back to the reg will make it overcharge. Ron

Yep it has the 70 and up regulator. I had the new regulator checked, and I made sure there were good grounds attached to the regulator. I performed your test and ran the proper jumpers and its still charging high at idle. What test should be next? If the grounds are good, the regulator is good, the wires are good, then it must be the alternator correct? Thanks for the fast response!

You need to see which field wire on the alt goes back to the voltage reg. I think its the green one but sometimes I have seen different colors. But you want to unhook the field wire going to the reg and see if it still charges. If it does then the alt has a grounded rotor and if stops charging the the field wire back to the reg is shorted to ground. You want the field wire that does not have 12 volts with the key on. Leave the 12 volt field wire hooked and unhook the other field wire then let us know what you get. Ron

So what is the actual voltage at the battery when the ammeter is showing this high charge condition? That's the first thing I'd check.