voltage pulse

Hi all a few weeks ago i installed a MSD 6AL and it works amazing but i now seem to be getting a pulse on the voltage gauge I have tried a lot of things i have read but can't seem to shake it any thoughts Thanks

This is a 71 you are working on? Important to say!!!

Harness voltage drop or grounding. Remove voltage regulator, clean around bolt holes and install with star lock washers. Same with Mopar ECU if you run that.

Check for harness voltage drop. Turn key to "run" with engine stopped. Stab one probe of your multimeter into the top of the PLUS battery post. Backprobe the ballast resistor the "high" or "key" side. This is the one the two resistor terminals are jumpered together. You want to see a very low reading, the lower the better. Zero is perfect, much more than .3V (3/10 of one volt) look for the cause

With stock wireing the functional path is battery.................starter relay stud..........fuse link.........through bulkhead connector (RED ammeter wire)..........to ammeter........out ammeter on BLACK.........to welded splice...........off to ignition switch............through switch connector..........through switch.........back out switch connector on DARK BLUE "ignition run" (color may be different some years).........out bulkhead connector.......and branch off to ignition, to VR, to alternator field,....electric choke,.......and some smog doo dads depending on year/ model.

If that is OK and I bet it ain't, fix it. One way is to use a relay, electrically cut the IGN1 "run" wire coming into the engine bay, trigger a relay with that. Feed power to the relay contacts off the starter relay "big stud" through a breaker or fuse. Take the engine bay end of the cut wire and connect to the load contact of the relay. Ground the remaining coil terminal.

Also check voltage drop between alternator and battery. Start car, run on fast idle, run heater, lights, whatever loads you can bring on. Stab one meter probe into battery PLUS. Connect remaining probe to alternator output stud. You want system charging "hard" under load. You might see as much as a couple of volts, but any more than that you need to check things

Functional path is alternator........through bulkhead connector.........to welded splice (BLACK)..........to ammeter...........out ammeter on big RED.........back out bulkhead connector.........fuse link..........starter relay.........to battery

If that does not fix it replace the VR

My 67 has later isolated field 60 amp alt' and solid state regulator (approx' 8 feet of blue wire added to the 67 harness). Those parts were taken from a 73 model donor laying here. Also mention Alt' gauge converted to volts gauge. Some time later, when the volt gauge suddenly presented a pulse, regulator was suspect and not going to break my bank. So I didn't attempt any diagnosis. New regulator cured it.

@Chuckster71 For a more specific response, knowing more details will be helpful. Where the voltmeter has been wired can make a difference on the readings.
Same with with the MSD's power supply. Any other modifications or electrical loads?