re-wiring former race car, starter not cranking Options

[RFoulds]

Car has been off the road for a while. jst got motor back from Jorge at European Motorworks in Hawthorne. freshly rebuilt. while motor was out, I rewired dash to eliminate some of the race car stuff like push button start with no keys. SO i have reinstalled stock steering column and ignition switch.
with motor back in, I have 12 volts to the starter verified by multimeter. but when I turn key, nothing happens. multimeter shows just 3 volts to the solenoid terminal connection from the yellow wire, and only momentarily when key is turned, not constant even if key is held there.
in rewiring the ignition, I may have missed something but, whoever installed the start button just hacked off the wires so it was pretty easy to just reconnect color to like color.

One possibility is seat belt interrupt. I know 74 had that, but this is an early 73. I believe it only has seat belt warning light. but, with the light not being installed, and the set belt switches not in place, would that interrupt the starter circuit? I can only follow wiring diagrams so far, flow diagrams are a mystery to me.
there is a yellow wire and two grounds at the rear of tunnel that were probably the seat belt warning light system. Does anyone know, if these interrupt starter circuit?