alright.. plug a MVS in, then at the jamma plug, look at the side which is facing the part which has 6 pins seperated from the rest by a missing pin ("key" hole), it's at the right if you look straight at the MVS board. kinda looks like this:
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the rightmost pin is pin 1, the leftmost is in 28, parts side (called that cause that's where all the chips are on the game board). the bottom side is called solder side (cause of the solder spots)
now you count to pin 12 parts side (that's the 5th pin after the key pin).. that'r R. next to it (pin 13) is B. on the solder side/opposite side of the R pin, you got G.
now unsolder the wire on those 3 pins (12, 13 parts side, 12 solder side), then solder a resistor to each of those pins and the wires to the other end of the resistor. that's it.