Start / Stop Power when more power is added
Some details are need on Tach voltage still. Let us know what is it is.
Red Yellow can be a string of 5 instead of 4 then use 330 Ohm to get say 30mA drop on LEDs ( OK for short durations)otherwise 20mA max.

You ought to buy Blue,Yellow and Red 5mm LEDs and wire them with Anode to +. Comparator or Op Amp that can drive 20mA is active when low output. I added Cap in middle and 60Hz sawtooth to simulate shifting thru all the gears.. forever...

BLUE is always on and serves as Zener voltage reference voltage to comparators and adds to dash lights.If you figure out where what the BLue Voltage is your can use the internal dashlights for this. But I did not try to switch them off.
Yellow is ON set by 8K resistor, Red set 25% higher.(10K)

zoom  Simulator