You don't want to use the White/Green wire as it supplies voltage on a constant basis which complicates things. All you have to do is (w/no key in the ignition) to turn the headlight switch to the first position and identify which Red/Green wire has voltage. Then turn the switch to the off position. Then jumper a wire from this Red/Green wire to the problematic R/B wire and your problems will be solved (I did something similar to this at the headlight switch and it has worked for close to 20 years). The only caveat will be the that the dimmer knob which controls the light intensity of the dash lights will also control the light intensity of the tails and side markers which will not be an issue if you just leave the knob to the fullest position.