Bad starter relay?

Stick, or stick with clutch safety switch, or automatic?

IE how many 'push on' flag terminals does the relay have?

ONE flag terminal means there is no safety device AND THE RELAY must be grounded.

TWO flag terminals means the second flag terminal goes "to ground" through a safety switch, either the neutral switch or the clutch safety switch

I see you say 69 Dart so that should not have a clutch switch, but is it stick or automatic?

START by probing the connector on the YELLOW wire flag terminal at the start relay. Twist the key to start and see if you have a light/ 12V

If so, move the meter to the second flag terminal which (automatic) goes down the firewall to the transmission NSS. This should GROUND in park or neutral

If you have power at the second terminal, IT IS NOT GROUNDING which is needed to activate the relay

OH............and check the transmission linkage.......Twist the key to start and wiggle/ move the shifter see if it cranks or "tries" to

Then go down and be sure the connector is installed on the transmission