Schwak, when you bridge the connection between the small and large wire on the starter, you are bypassing the ignition switch, which serves the same function.
Shorting the connection (screw driver or IGN switch) pulls the bendix (starter drive) to engage the flywheel while the motor starts to spin, starting the engine.
I would start at the ignition switch, which typically suffers from several kinds of failures:
Contacts defective to the starter, resulting in a no-start condition. Try twisting on the key a little harder than normal and it will sometimes force a connection, but the switch would still need replacing.
Engine tries to start, but shuts off when the key is released, because the contacts to the injector pump "run" switch are not engaging.
The injector pump shut-off (or Run switch as some refer to it) switch can fail, inhibiting fuel to the injectors - but the engine will crank over...
Hope this helps.
S