I think I made a mistake in my drawing.
C1 was added to increase starting surge (if needed) to pull in current relay.
Or maybe I had some other crazy idea that I no longer see.
In reference to email:
As others may be following, I'm posting here.................................
This is a very simple circuit, but it will need fine tuning for your exact motor load.
This picture is the same as the diagram I posted.
I don’t think I can simplify it more.
When connected thru your switch as shown:
Cut the neg. lead to motor and run current thru the large winding of the reed switch.
When the motor is running this current will form a magnet, closing the the circuit between the two small wires.
The motor is started by turning the switch on until motor starts.
The two small wires will keep the motor running after you turn the switch off as it is connected across the start switch.
If motor current drops, magnet weakens, and the contacts open inside the plastic tube (reed switch), stopping motor.
Until switch is pressed again.
The diode is needed to protect the switch as it’s only good for a few 100 mAs of current.
If your motor draws more it will destroy the switch inside.