That is the dash light dimmer control switch.. Rheostat = Dimmer. Bright to dim.
Please check the fuse first. If the fuse is good then the rheostat switch is the next component to test. The rheostat is the dimmer switch you use to control the brightness of the dash lights. It will probably be part of the headlight switch. Best of luck.
Most likely reason is the rheostat on the gauge cluster that controls the dash lights. On the backside of the gauge cluster connected to the LH knob is the rheostat. It was built really robust and can usually be disassembled can cleaned. Hope this helps.
First of all, are the dash lights also out......if so, the rheostat behind the instrument cluster may be the cause........
Check fuse for parking/tailights Could be bad dimmer rheostat Could be bad headlight switch
Check fuse for parking/tail dash lights Could be an open in dimmer rheostat
2 are the instrument light dimmer buttons and the other is 2 reset the service light
Bulbs burned out? Dimming rheostat is open? Bad headlight switch? Make sure parking and tailights are working (same circuit)
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Check fuse for parking/tailights Check the rheostat dimmer switch
There is a adjustment to dim the dash lights the adjustment may be turned dow, some models have a wheel type switch or similar, check owners manual. It is called the rheostat.
Try turning headlight dash dimmer rheostat to extreme end
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