If it is on a manual tranny it is the signal for the optimum time for you to shift for best fuel economy.
this is used to get best fuel efficiency. in manual gear it forces the driver to change from first into forth gear
the reverse light switch is either out of adjustment. or broken. new one should be fairly cheap
One down, four up.
If the harley has a four speed tran. One down, three up. Five speed, shift one down, four up.
under passenger side of dash remove panel were interior light is and you will see fuse holder with four fuses
Sounds like it may have been replaced at one point with an inferior piece.
one down four up
one down four up
One down, four up
Down one, up four.
Change the bulb and check to see if it's not grounding out.
There are many places one might go to find specifications on shift lights. The most reputable resource for individuals would be an official shift light website.