Looks like corrosion on the Black/White + wire. The Yellow/Red goes to the Starter Relay.
Clean it with some baking soda and a tooth brush.
VERIFY in NEUTRAL >> If you take a wire or something bridge across the contacts for the above wires.
Starter relay should operate if the IGN switch is on and you bridge the contacts.
Is the "shunt" moving freely??
The shunt is a sliding bar that makes a connection across a pair of contacts.
This sliding bar can move up or down a bit in case the contacts move some from being hot.
Sometimes a knife has to be used if plastic melted on the shunt carrier.
Stretching the spring a little may give it the tension it needs.
My brother in law's cleaning did not fix his Starter Switch, trimming plastic fixed the problem.
Use a non-abrasive cleaner to clean the contacts.
Kitchen cleaning pads are good.