Dash gauge lights -- change brightness w/ headlamps?

[2009 Tacoma AC SR5 Pre]

I am trying to remember how the instrument panel lighting is supposed to behave as you change the headlamp switch position and the gauge dimmer.

The clock beneath the radio will go dimmer with the headlamps on, and bright with them off. I could almost swear that I recall my dash gauges doing the same thing -- dimmer with headlamps, brighter without. Recently I've noticed the gauges look very dim in daylight -- so much so that I went to turn off the headlamps, but they were already off.

So I tried cycling through settings. The odometer behaves as the clock does -- brighter with headlamps off, dimmer with them on. But the lighting for the gauge numbers does not change at all.

Using the gauge dimmer does dim the lights behind the numbers and the odometer as well. Turning it all the way up to maximum brightness, the numbers are still pretty dim for daylight.

The only thing I have changed recently was installing a new radio last fall. The dash harness was not altered, I used a plug-in adapter harness. I suppose it is possible that I could have damaged something while I was doing the work. It's also possible I didn't notice the brightness issue until this summer, because my job hours in fall and spring mean I'm almost always driving in the dark or near dark.

Am I misremembering how the gauge brightness is supposed to behave?

 

I don't think you are. I'll take a look at mine when it gets dark tonight and report back.

It's possible that your stereo is causing too great a load on the lights, instead of a high impedance voltage detector. I know it's not convenient, but perhaps you should attempt to disconnect your harness from the radio and see if it changes the behavior.