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Paul M ASE Master
Paul M ASE Master, ASE Master Tech
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Chevrolet Suburban 1500 LT: I have a 2002 Chevy Suburban.

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I have a 2002 Chevy Suburban. My dash lights go out when the headlights come on. I have checked the voltage at the ILLUM fuse and it does vary when I turn the dimmer up and down. What else should I try?

Hello I'm Paul and I will help you with an Answer to your Question


there is a common failure with the headlight switch that causes this problem


I am attaching the testing information


click here to view test


suspect a bad headlight switch


Remember to rate my answer positive so I get credit for my help.


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Customer: replied 3 years ago.

Hi Paul.


I retested the voltage at ILLUM and now don't see the voltage vary when I turn the dimmer up and down. I'm pretty sure it did that before.


Jumping the Orange and Light Blue wires behind the switch had no effect. I assume it was the larger Orange that was indicated (there is also a smaller one). The clock light went out as it does when I turn the headlights on.



does the orange have 12 volts on it?


When you jump the Orange 12 volts to the Light Blue does the dash Light up?


does the ILLUM fuse have 12 volts to both sides with the Orange jumped to the Light Blue?

Please answer the above questions and I can tell you the next step in testing



Customer: replied 3 years ago.

Both Orange wires have 12V. The larger one is in the "B" position. The smaller one is not labeled, but would be "D". The Light Blue is "A".


Jumping Orange "B" to Light Blue "A" causes the clock light to go out. I do not see any dash lights. It is daylight, so I'm going by the clock light.


With the jumper in place, there is no voltage on either side of the ILLUM fuse. One side causes my digital meter to fluctuate, but mostly in the mV range.


the light blue feeds the ILLUM fuse


if you jumper power 12 v to the Light Blue from the Orange and the ILLUM fuse has no power the Light Blue wire is broken between the headlamp switch and the ILLUM Fuse


are you sure your getting a good reading on the fuse?


if no power on the fuse ILLUM but power at Light Blue then the wire is broken somewhere between headlamp switch and the fuse... (often problems occur inside the fuse panel under the fuse...

take a 12 volt jumper wire and touch the fuse the dash lights should come on... if so you need to find the open circuit in the Light Blue wire between the headlamp switch and the ILLUM fuse


I am attaching a wiring diagram so you can see how it runs

click here to view

let me know what you find and if you need more help



sorry for any confusion but looking at the diagram


the Light Blue first feeds the INT Park Fuse #24


does this fuse have power? with the light blue jumped?


disregard the last message test the INT Park Fuse rather than the ILLUM fuse



I just studied the diagram in depth


jump the Orange to the Dark Green B to K


does the ILLUM fuse get power and dash light uP?

if so but it does not with the headlamps on and dimmer turned up the headlamp switch is bad


sorry for the confusion I had to dig into multiple diagrams to get this figured out



Customer: replied 3 years ago.

Okay, I will go test this. It's a bit of a walk, so sorry for the delays between messages.


BTW, jumping the Orange "B" to the ILLUM did light up the dash, so we're making progress.

ok let me know what you find

Customer: replied 3 years ago.

Jumping Orange "B" to Dk Green "K" did cause the dash lights to come on. Are you sure this indicates the switch is at fault? Why did the first document you linked instruct to jump the Lt Blue?

the original diagnosis was from a technicians database


the Light Blue is for illumination when park light relay is on


the Dark Green actually feeds the Illumination fuse


it gets 12 volt feed from the Orange wire through the Switch when (Park or Headlights are on) to the Dark Green


if Orange has Power


and Headlight switch is on and Dark Greek does not get power coming out of the switch with dimmer set to on position then the Headlamp switch is bad.

Power from the Orange 12 volts... runds Through the headlight switch/dimmer to the Dark Green ..


so if you plug in the headlamp switch and turn headlight on there is no dash lights


but if you jump the Orange to Dark Green they come on Headlamp switch is bad for sure


sorry for the confusion but not sure who wrote the original diagnostic I attached


but the headlamp switch is bad



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