disconnect both ... small wires on the selenoid.
turn the start key to ON one wire will have 12v measured against theengine unpainted body & none on the second one.
if you do it is a miracle.
Connect
ONLY the wire which had the 12v to
ONE of the control post of the selenoid...
take a NEW piece of wire & wire it on the other small control post and ground it to an unpainted section of the engine .
if it does run the starter while the key is at START your original selenoid ground source is no good ... needs a fix .... find solid ground via or not... any safety device & retest
if the selenoid does not activate the starter you have 6 options
a - BAD highly resitive volts from the key.. find & fix resistive path
b- BAD SELENOID internal winding ....no clicks
c- BAD relay contacts inside the selenoid... clicks but does not pass high
amps to the starter.
d- bad corroded - broken high amps red wire from batt to selenoid or selenoid to starter
e- bad starter
f- replace engine

or find an old dealer
" patience brings joy"