Solution: Laptoptablesaw :-)
Another power-tool in the closet I use from time to time is the Proxxon Disc Sander.
Then it hit me. All the other Proxxon tools I have uses direct current motors (DC-motors). DC-motors is easily reversed. The two wires to the motor should just change place.
The backcover was unmounted and yes the motor was a DC-motor and better there is lots of space for mounting a switch besides the on/off switch and speed-controller.
The red and black wires from the circuit-board to the motor is unsoldered and replaced with two new wires that goes to the switch.
In the process I pulled too much in the wires so the speedcontrol broke. So unsoldering the white and black wires is a good idea :-) It doesn't matter how the white and black wires is soldered back to the control.
A little theory: Reversing a DC-motor.The switch used is a Double Pole Double Throw (DPDT) switch.
DPDT switches are available in 'toggle' or 'slide' types, as shown in the picture below. Both types have six connections - three for each pole of the switch.
This circuit shows how to connect one DC motor to a DPDT switch.
At last my Proxxon disc sander with a new miterguide.