69 Charger electrical question

[sixt9rsx33]

So I ran a jumper from the battery negative to the ground wire that runs from the blower motor to the firewall. Still no help with the tach jumping around.
All the screws are in place under the steering column cover. I will poke around under the dash next looking for a unattached ground wire. Any other ideas I am all ears.
Tinkerman, I hear you about the alternator.
L

[sixt9rsx33]

I still have this issue. I suppose will confirm belt is tight and dig a little deeper into the dash. I need to confirm my alternator is the correct amperage. Thanks for the suggestions so far.