Height Gage DRO

Upon further inspection of the old Mitutoyo height gage, the only way
to bring it back to life is to convert it to a DRO.
Evidently it had a dedicated "box" to run the LED, etc that is no
longer there.

To my delight I found that it simply contains a set of gears that turn
what looks like a standard glass encoder disk, except that the disc
has 2 sets of concentric encoder lines and 2 LED's
Is there a standard for wire colors to the LED? Is black always neg?

Does the 2 sets of encoder lines give higher resolution, or is that a
way to keep absolute reference?