Sorry for the late reply. I didn't get your PM? Don't know why.
In my experience, some TVs need more than 5v, some don't. You might get lucky. You would have to test each one to be sure. But the technical specs say that the 4:3 AV mode switching signal to pin 8 should be in the range 9.5v - 12v, and 5v is simply lower than that so what more can I say.
That is why, when I make a full-on VGA-SCART cable, I always add on a standard 4-way PC molex power connector to supply:
* 5v (the red wire), stepped down by 100ohm resistor to about 2v, to pin 16 (triggering RGB mode).
* 12v (the yellow wire) direct to pin 8 (triggering 4:3 AV mode).
* DC Power supply grounds (the 2 black wires) to pin 18, to make sure all is safe.