Since there was some interest, I'm going to present some pictures of my "special power switch".
I just reopened my Vectrex and saw, that I did not only cut the 5 VDC, but more thoroughly , all three voltages, with a single three layer on/off switch, which can bought in any electronics shop. It is a very simple job, which can be done by almost anybody with some basic mechanical and electrical skills. Or maybe you can still find some radio and television technician, whom we used to have anywhere nearby - back in the day, when tv-sets were being repaired and voltages higher 3.3 volts were not considered rocket science.
Unplug Vectrex and remove the five screws that attach the back part of the housing:
There is the switch, simply mounted into a hole drilled into the front part of the housing:
The LOGIC BOARD'S voltages are supplied by this connector coming from the POWER BOARD above.
yellow: -5 VDC
orange: +5 VDC
red: -13 VDC
I disconnected the green GND line to open up an inductive ground loop which is introducing noise and hum into the circuit and replaced it by a short, thick ground connection (the yellow one on the next picture).
As always, cables are too short. I had to attach extensions to the three voltage lines. All three are connected seperately to the three layers of the switch.
On the other side of the three switching contacts, three wires directly lead to the POWER BOARD and are soldered into the proper positions. There are labels printed right onto the board:
That's all! Just close the Vectrex with the back cover and keep an eye on the BRIGHTNESS knob, which has to fit into the hole on the backside of the Vectrex - no forceful pushing required.
The only time, I'm using the regular Vectrex power switch is when I'm starting or stoping to play Vectrex. Each time I change games I only switch off the computer part and leave the television part on, prolonging it's life. I fear in the age of flat LED tv-sets, it will be going to be harder and harder to find any classic television spare parts.