On my toyota 4 runner I had the same prodlem
I think it is in the wire harness at the ignition swicth
not the ignition swicth. but were the wires make conact in the plastic houseing.
I did put new wires (but not the houseing) this helped
but it didn't solved the problem it's in the metal contacts.
I replaced
The starter
The cables 2ea.
The battery
The ignition swicth
The wireing
The only thing left is the plastic mount for the metal
contacts behind the ignition swicth.
This only what I think.