On my '67 Fury III 318 engine, I have been having problems keeping the battery charged. I replaced the alternator with one from Autozone (45 amp double pulley) about a year back. I had them test the alternator recently and it passed. The battery is a Napa 72 month which is 4 years old. I took it to Napa and it tested good. If I charge the battery with my portable charger, it is good for two to three weeks. I checked the battery with the engine running and got about 12 1/2 volts with the engine reved up. Then I looked at the meter and it read a little over 13 volts at idle. It raised up slightly when I reved up the engine but then was back to 12 1/2 again with very little increase when reving the engine.
I am using the grounded brush system with an upgraded solid state regulator. Could it be a poor connection possibly in the bulkhead connector. HELP! Any info will be most appreciated and I aopligize for the long post.
John

1st I'd put it on a fast idle w the a/c lights/stereo going & see the diff in voltage from the source (alt) and the end destination (batt posts). Voltage drops may be excessive and may need more alt (85 iirc M body has 78 amps w dual field terminals, ground one like you already did

did this start recently? or has it always done this?

what was the last thing you changed?

good ground at the vr?

sensing voltage at the vr?

The problem has been going on for several months now. It was fine before. Should I check for voltage at both of the VR terminals and should they both read 12 volts? I have always had the amp gauge dip down at idle especially with the lights on but my other '67 Fury does that too but I am not having this problem with it. Shouldn't I be getting a voltage reading at the battery of 13 - 14 volts ideally?
Thanks guys for the help.
John

check the battery to rad support ground and to engine- take both off and clean them up good. and as well as the bolts at the VR too.

if still not charging at above 14 volts at 1500 rpm at the battery- let us all know where to check next!