VDO gauges not dimming - any suggestions?

[butters]

I'm wiring in a couple of gauges at the ashtray, VDO oil psi & temp. I want to do it as cleanly as possible, and ideally retain dimming to match the dash.

I ran the lighting wire to the headlight switch and tapped to the switch backlight bulb there, because it was easy to get to. However, the vdo backlight bulb does not dim and just stays at max brightness. Is it a bulb thing? It's not an LED bulb just a standard incandescent.

[reelizmpro]

Why did you tap there when the ashtray light is literally right there and it's on the correct dimmer circuit? I'm not sure if that particular backlight bulb is dimmed or not but I know the ashtray bulb is.

[butters]

I tried the ashtray bulb first and you're probably right, but it didn't dim for me. My ashtray bulb is burnt out and I'm not going to be using it anyway, so I then went to the switch where I know the dimmer is located and I could see the bulb dimming. No luck though.

[Dirtboy]

The bulb you used at the light switch is always on with the ignition; never dims. Thats why your gauges won't dim. Use one of the other light circuits.

[butters]

It does dim - I checked before moving my splice over to it.

I may have the answer from googling and finding a thread on s14.net.... the dimmer is a function of ground-side resistance change rather than hot-side thus I need to ground the bulb on the same ground circuit as the dimming lights.