electrical issues with the 67 fish

This is a pic of the starter relay in my -67 4-speed.
If you jump a wire from the positive of the battery to the spade of the (arrow)yellow wire, then it should turn the starter, if not try to ground the relay housing.
If it (starter relay) got a fourth spade try to ground that one (nss).
The black wire goes to the starter solenoid. The red fat (not connected to the starter relay) one goes direct to the starter motor.
As Longgone mentioned, have a look at the bulkhead connector to see if you got a bad connection there. seems as you´re dropping a few volts there.
However 9.6 V might be enough to make the starter relay to "respond".

start relä 004.JPG