If we can tap voltage input to tacho's coil, then all we need is an analog comparator with a variable resistor to determine which is the comparison point to flag a "higher than reference" condition. This is the low-voltage stage. Run the output to a Schmitt trigger (positive feedback op-amp only) to turn the signal into a higher-voltage on or off instead of a variable signal, and to a voltage-follower amp (buffer op-amp) to drive a lamp.
I think this entire circuit can be designed from a few op-amp ICs.. but since the moving coil input voltages are usually very small, that will mean we'll need a small reference voltage also.. so we might need a low-voltage reference output IC also, e.g. a temperature-stable 2-volt reference IC.