question for electrical guru's ( not motorcycle related )

[downsouth]

My boss has a 2008 Gmc Sierra Pickup with daytime running lights. The dash lights work fine during the day, but at night the lights in the gauge cluster will not work. He took it to the dealer and they said its was the sensor on the dash by the windshield, changed it no different. The sensor is working ( will turn lights on and off ) My question is it has 2 wires on it if I swap the wires around in theory wouldn't the lights work the opposite of what they are now. Any input helpful. Thanks. Robert

[05RedKat600]

No. Swapping the wires around wouldn't change anything on that sensor. Matter of fact, it most likely wouldn't work at all.

The way that sensor works is that when exposed to sunlight, it produces XX Volts. At night, it produces no volts. The relay/ecu uses that voltage signal to know when to turn the lights on and off.

Do the lights work when he manually turns his headlights on?

[downsouth]

The dash lights don't work with the head lights on at night either. this thing is driving me crazy.

[Wild-Bill]

...when exposed to sunlight, it produces XX Volts....

Picking nits here, but does the sensor produce voltage or does it vary in resistance? Only reason it really matters is how you test and connect it. If it's a photo-variable resister then testing is easy and it won't matter which way the wires are connected. If it's a photo-voltaic cell then the wiring connection is critical.

Downsouth: If he turns on the headlights (at night) do the dash lights work? If so then the lights not working at night may just be a "design feature".

[05RedKat600]

Picking nits here, but does the sensor produce voltage or does it vary in resistance? Only reason it really matters is how you test and connect it. If it's a photo-variable resister then testing is easy and it won't matter which way the wires are connected. If it's a photo-voltaic cell then the wiring connection is critical.

Downsouth: If he turns on the headlights (at night) do the dash lights work? If so then the lights not working at night may just be a "design feature".

They can do either Bill. Depends on if they used a Photovoltaic or a Photoresistive cell. Either way, switching the wires won't do jack, lol.

No dash lights at night means a bad fuse or something. Possibly a bad switch too. Without seeing a wiring diagram, I can't be all that much help.

[downsouth]

Downsouth: If he turns on the headlights (at night) do the dash lights work? If so then the lights not working at night may just be a "design feature".[/QUOTE]


no they don't work then they only come on in the daytime

[05RedKat600]

Well, the wiring is somewhat independent for the daytime part. The good news is that you know the bulbs in the dash are good. Seriously, time to check the headlight switch and wiring. There also may be a relay involved that is faulty, not allowing the night time lights to come on. Let me see if I can find a schematic somewhere.

[downsouth]

one more thing he said that when he applies his brakes they will blink on then back off.

[05RedKat600]

At this point, I'm thinking there is a controller box of some sort for the lights, and it has a short. The only other thing is that his foot is hitting a connector when he presses the brake pedal causing the lights to flicker. Check under the dash for loose connections.

[downsouth]

Thanks for all the input

[05RedKat600]

If I could find a schematic I could be more help. I just can't find one.

[downsouth]

yeah I been looking for a few weeks and can't find anything I did a check on my 2003 Trailblazer and when the sunlight hits my sensor my dash lights go out. just the opposite of his so at this point i'm kind of calling BS on the dealer changing the sensor . Thanks

[rexazz2]

pull out the cigarette lighter and check the element on the end
NO I AM NOT JOKING
GM did some stupid electrical things over the years
I know at one time the element would break off the end of the holder vibrate around the socket , short out ,reset self reseting breakers ETC

If its not that
There will be a module in the dash that controls everything , it probably has a broken solder conection
I am away from the trade but at one time I would have had an answer within moments from a licenced GM tech
EVERYTHING here for several years now has day time running lights
Those kind of favors are getting harder to get

[92xjunker]

has same problem with GMC van, check the dimmer control for bad connection or broken solder joint. may be a bad lighting control board. Every thing in modern vehicles runs through a control board of some sort. had to change lighting control board on my van.

[Astro4x4]

Bad dimmer control or bad Body Control Module (BCM)