per '70 Plymouth Service Manual:
Instrument Panel Wiring Diagram - Belvedere

Ignition Switch Lamp Ground:
M6A-18Y* & M6B-18Y* (18ga. yellow w/tracer)

&

Headlight Warning Buzzer:
L6-18Y* & L6A-18Y* (18ga. yellow w/tracer)
Q13A-18R & Q13B-18R (18ga. red)