Some Reslo RB mics have a transformer with a split secondary that gives the owner the choice of either a 30 ohm or high impedance output. Often these mics get dismantled and rewired, so here is where the internal transformer wires go….
For a 30 ohm output, yellow is the ‘hot’ output, and should eventually end up at XLR pin 2. White is cold, and goes to pin 3.
The green wire should not be grounded, but this sometimes happens by accident if the plug uses one of the pins for ground. The result is a high impedance path to ground from the output, which can act as a filter and give a weak output and weird frequency response.