eletrical gauge setup (probably easy q)

[Sierra4x4]

Just got a sunpro oil gauge with the built in light. Ive tried hooking it up to the fuse box but i havent had much luck. Id like it to come on when i turn on all the other gauge lights. Ive tried the headlight fuse and it just stays lit all the time. (since it runs to the dash switch it makes sense) I could put it in the ignition fuse but ive already got fog light switch in it and would rather not plug something else in it. How can i get it to come on when the rest of my gauges do?  

[73K20]

I wired in the same oil pressure gauge in my truck.  I wired the light to the light that illuminates the climate controls.  This is the only interior bulb that is controlled by the dimmer switch and has wires which can be spliced into.

1973 K20 - 350/350/205