Problems adding gauge light to dashboard dimmer switch

I added a Boost Gauge to my 1999 Tacoma SR5 and I'm trying to hook the light for the gauge into the wires for the dimmer switch that controls the dashboard. This way when the dash is lit, so will the gauge - and visa versa.

I'm connecting the light for the gauge right at the plug for the dimmer switch and I've identified the wires delivering power and ground with a test light.

I've successfully identified the wires I need to splice into, however the issue I'm facing is this:

When the light bulb for the gauge is connected to the wires of the dimmer switch and the dimmer switch is set to maximum brightness, the dash is on as usual but the gauge is totally dark. Additionally, when the dimmer switch is set to minimum brightness/off, the dash is totally dark but the gauge bulb is bright and fully lit.

Why am I experiencing this and how do I fix it?

 

Just a guess, but I ran into this in my house. Is the bulb on your gauge dimmable?