Tylus, it's a feature on the auto headlights. The headlamp switch is in the auto position, the wipers are activated and the headlamps come on. It's not because of the ambiant light. Turn the wipers off and the headlamps turn off. We know this because all of the dash lights and nav screen change when the headlamps are on/off. I guess one would have to remember that this is a "Limited" model with all of the bells and whistles sans a sunroof.
I rainx my windshield, which means that unless it's a torrrent or I'm running with a truck on the freeway with lots of tire spray, I don't use the wipers. That would answer the question of the lights operating because of the darkness of the storm.

 

Let us know your experience with installing DRLs, it's an option I didn't know was available until recently and I'd like them.

-- Chuck

 

Tylus, page 102 of the 08 Expedition owners Guide, explains the wiper/auto head lamp function.

 

Went digging through my Owners manual...and then went here http://www.motorcraftservice.com and looked at the 2008 manual.

Nada. and I have a 2008 Expy EL Limited with all the bells and whistles as well. Maybe it's a build date thing? my Expy was built in Sept 2008 (I think).however, I did find the Auto-lamp + wiper feature is/was available on 2009 models. that is pretty cool I guess. I'd rather have the DRL module installed personally. Lights on 100% seems better than just whenever the wipers are on.


thx for the correction though. gotta keep that feature in mind for when I upgrade to a 2011 or 2012 Expy

 

Just tested this yesterday, our 08 also turns on the lights with wipers. Love this feature on my 300, just wish it had rain sensing wipers too!