More puzzles 740 gl

Any idea why the engine could speed up when I pull the starter solenoid
switch Wire off and slow down when I put it back and it does not seem to
engage the starter while running.
Lately the car fails to start sometimes and I have to manually connect
solenoid terminal. but when I replace spade connector the engine slows.

 

That's a weird one. I wonder if you have a bad ground connection to the
engine block? Often bizarre electrical gremlins can be traced back to
bad grounds, it causes current to find other paths to ground, sometimes
through other devices.

 

It is puzzling me too, If it were a bad ground connection I would expect
problems with the high current in starting.The car goes long distances
without blowing fuses.I might measure current on the solenoid switch
wire. Some other current consuming device may rely on the wire being
connected.I could try driving with it off and see what happens.