So I noticed my truck has a sensor on the backside of the mirror. I've guessed for nowthat it's for the auto-dim feature?

It however looks very similar to the sensor that would be used for auto headlights, as my Hummer has. If that's what the sensor is for, does anyone know of a way to make that sensor work to automatically trigger our headlights? Does someone want to look into this?

 

You can use the dei 545t nite lite box to automatically trigger your head lights.....

 

Does that unit require it's own sensor?

 

The sensor you are talking about is for the dimming mirror, so you were correct with your assumption...

Yes, the DEI unit has it's own sensor to detect daylight. I definantly like mine....

Here's a write-up I did on the install: DIY Automatic Headlights: 06, 07, & 08's

 

Hmm... how big is the light sensor on that unit and where does it go?I'd rather not have to install another light sensor if it's going to be an obvious box.

 

On my 300C, it's a small plastic dome on the dash near the windshield, smaller than a quarter and about 3/4" high. I think the sensor that comes on the DEI kit is similar. The sensor in the mirror is probably the auto-dim. Could be for the smart-beam, too.

 

On the DEI unit, it's about the size of a nickel. You can pretty much put it wherever you want. I hid mine in the unused speaker hole in the front of the dash, you can't see it, however I don't have the infinity sound system, which is what the speaker hole is used for.