Thanks for all of the photos! I was able to reference a '73 Charger with a factory tach and the hole with plug was in between the M/C backing plate and the harness block. On my '74, the harness plug that goes through there contains all of the A/C wiring that goes out to the engine bay. Must have been a change after '73. Does any one happen to have access to a '74 that may have had a factory tach? Thanks!