before 4 years i experienced the same problem with the reserve switch. I am sure that the bulb in the tacho has nothing to do with the fuel pump. i am 100%. you have a bad cable. i had the haynes service manual and sorted out which cable was. it beggins from inside the left scoop(where the flasher) there is a big (i don't know which is the exact term) plug under the left scoop. one of the cables i cannot recall the color as i have not have the manual with right now but this causes your bike to work only is res mode. i just installed a new cable over it (bridge) from the plug under the left scoop to the other end (at least as far as i could reach without tearing apart the wiring harness) and i was suprised that this was the problem. you bulb has nothing to do with it.
