Need illumination wire for aftermarket tach!

[YOUNG SCOOTER]

I am trying to wire a aftermarket tach and need a 12v illumination wire for the gauge. Where should I go to splice into this? Apparently the dash dimmer switch is an adjustable ground and won't work. And I'd like to not just stab the illumination wire into the keyed hot like most people do

[YOUNG SCOOTER]

It's a 2008 Yaris hatchback 5 speed 2 door car. Gauge is the standard 4 wire gauge with keyed hot, illumination, ground, and signal. I've got all the wires except illumination

[YOUNG SCOOTER]

The only Idea I have at this point is a relay that is powered off of the parking light circuit but I'm still not sure where to grab that.