That hanging wiring harness should tell the tale if correct 70 4 spd harness or not.
On a 1970 the light is mounted in the plastic housing as is seen with yours.
Because of this the wiring to the light should have a black wire with white tracer for bulb,
plus a purple wire to ground it as seen in picture provided.
68-9 were in a steel frame and had no need for ground wire, had only one , the light grounded itself.
Let us know what your harness shows.