I used 3 wires for this mod, GND, VCC 5+,
and the 3rd to the 8th pin of the 74HCU04 IC.
I powered a Attiny85 from the 5V, and connected the 74HCU04 to a
input on the chip.
The 5 millimeter light pipe holds the RGB LED in place,
which has the MCU soldered directly to it.
On the software side when the 74HCU04 output goes high, the LED turns on, when it goes low, the LED turns off.
So when the reset button is pressed, the LED will go off, or if the game cartridge can't be detected, the LED will blink.