Re: Ignition Coil with points - yellow wire disconnected?
The yellow wire "bypasses" the resistor wire so you have more voltage going to the coil when the solenoid/starter are engaged. When the solenoid engages it sends battery voltage to the + term. of the coil. Since the starter motor turning over the engine puts a high load on the battery dragging the voltage down some, having only the resistor wire going to the coil and dropping the coil voltage even more can make for a weak spark and make the car harder to get started. The ONLY time the yellow wire comes into play is when the solenoid is engaged when starting so it would have no effect once running. The only problem that you'd have with it disconnected is a weaker spark when starting up which may make it a little harder to get it going.