Bentley manual indicates there should be 3 wires to the OXS
Elapsed Mileage Counter (#49).  These should be Blue/Green
(blue with green stripe) which lights the OXS lite and solid
Blue, which connects it to the Alternator LED for testing
during startup.  Brown of course is ground, and when the
switch in the unit trips, it provides ground to the warning
light through the blue/green wire, enabling it to function.

Can't see much reason for disabling this unit unless a diode
somewhere failed--there is one in the counter and one in the
dash--or something else just shorted.  Or perhaps it just
tripped prematurely and the PO couldn't decipher how to
reset it--eliminating the connection between brown and
blue/green will do it.