Instrument dimmer rheostat question.

Hey guys, I bought a nice Auto Meter oil gauge and hooked up the wire leads for the internal bulb directly to the two wires coming out of the instrument dimmer rheostat. With the leads on one way, it lights up opposite of the main instruments. For example, with the main instruments on bright, the oil gauge is dark....and with the oil gauge full bright, the main instruments are dark. If I reverse the leads, the oil gauge does not light up in either position of the rheostat. Anyone got any input on how to hook up my oil gauge so that it dims "with" the main instruments?

 

the wiring for the aftermarket light probably isnt able to carry different loads so its either dark or bright no in between...I have full autometer gauges (tach,speedo,water temp,oil pressure,fuel level) and they work like that either full on barely lit or off LOL