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Ask GM Tech (Cam) Your Own Question

GM Tech (Cam)
GM Tech (Cam), Chevy Technician
Category: Chevy
Satisfied Customers: 27664
Experience:  GM Grand Master Technician 2007. 11 years experience.
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2002 Chevy Tahoe: daytime..lights work..headlights..Instrument panel

Customer Question

I have a 2002 Chevy Tahoe, in the daytime the dash lights work. At night when the headlights come on automatically I loose all dash lights. Instrument panel and radio lights are gone but all still function.
If I manually turn on the headlights I also lose all dash lights. I can not figure out what relay is causing this, I am assuming it is a relay.
Submitted: 4 years ago.
Category: Chevy
Expert:  GM Tech (Cam) replied 4 years ago.

Hi, I'm Cam. May I ask your first name?
I am working to get you a fast accurate answer. About your vehicle,Does the dimmer do anything in the dash?


Customer: replied 4 years ago.

Hi Cam I am Robert,


The dimmer acts oddly, with the headlights off in the daylight it seems to do nothing. With the headlights on in the daylight and the knob all the way down I lose the radio lights, all the way up and the radio lights are dim. Turn off the headlights with the switch all the way up and the radio lights are bright. the lights for the shifter do not change at all in the daylight. At night with the headlights on automatically the dimmer seems to do nothing. there are no shifter lights, no radio lights and no instrument panel lights

Expert:  GM Tech (Cam) replied 4 years ago.

Do you have a test light to do some diagnosis Robert?


Customer: replied 4 years ago.

yes I have a test light and I have a digital meter also, however my wife just left in the Tahoe to take my son to a birthday party and will not be back till late tonight.

I will not be able to work on it till tomorrow.

I am retired, up until 2004 I was building NASCAR short track cars out of my shop here at my house. The electrical system on a race car is much more simple than my wife's Tahoe... My engine tuner who was a mechanic for 45 years and recently passed away once told me I had more tools than he did, He was worth .3 seconds per lap when he tuned our motors at the track on race night. Nothing will replace a great mechanic!

Expert:  GM Tech (Cam) replied 4 years ago.

No sir, Which team di dyou build for?

Do you have a schematic for this system?


Expert:  GM Tech (Cam) replied 4 years ago.

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Customer: replied 4 years ago.

The led dimming buss, where is it at? there is one fuse and relay panel under the hood and one on the left of the dash.

Also since the only time the lights do not function is at night how will I effectively test to find the failure point?


Also since auto shop, wood shop and metal shop no longer exist in high school around here I am looking into creating a racing club for High School kids. I have 2 race cars I could start them off with but I am trying to figure out where to get a grant or sponsorship to pay for it. I fugure it will cost $90,000 the first year and a half, if they dont crash too much. right now the its hard to get money out of anyone.

Expert:  GM Tech (Cam) replied 4 years ago.
That buss integral to the left dash fuse block. They are not like the old ones with the wires and pins that ht the fuse legs.
Customer: replied 4 years ago.

Ok then, what am I going to test with the test light?


Also some of the relays in the Tahoe have diodes and some have resistors. I had assumed that I had a bad relay that was causing the lights to act differently at night. There is one relay on the left side of the dash but it does not indicate what it is for, is this where I need to start?

Expert:  GM Tech (Cam) replied 4 years ago.

Test at the BCM. Take The trim off under the steering wheel, In the light blue connector, the purple white wire is the one that feeds the vehicle.

Also test the light blue wire out of the headlight switch for power with the park lights on.

Test the dark green out of the headlight switch for changing power with the dimmer dial.


Customer: replied 4 years ago.
BCM? what is that? probably something obvious but its been a long day and I am brain dead.
Expert:  GM Tech (Cam) replied 4 years ago.

Body Control Module, it is under the steering column on the dash.


Customer: replied 4 years ago.
I will be back in touch tomorrow when I can work on the Tahoe, thanks
Expert:  GM Tech (Cam) replied 4 years ago.

Sure. Have a great evening.


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