ground strap on A body to motor??

My Duster had a ground wire from the motor to the fire wall (S6) as well as the wire between the heater and wiper motors. I ran a strap between the block and firewall (bell housing bolt to heater motor stud) when I dropped the 440 in. I also retained the wire between the two motors. I would definitely run one if it's missing.

It might also be worth looking at your ignition switch. I have an old Dodge truck where the ignition switch doesn't always make the connection when it moves from the start to the run position. Sometimes the gauges are dead till I manually rotate the switch farther towards the run position.