I just removed the stock running boards on my '99 D2 and as I was crawling back underneath to admire how much easier it is to access the underside of the truck I looked up and saw this:




It's directly under the passenger side front door and was obscured by the running board. There is nothing like it on the driver's side and the truck runs just fine. I don't know what trim level I have so perhaps its something that's wired up but not installed on my trim level? There are two posts directly underneath where its obvious something should go. Thanks for any insight!

 

Photo didn't post :/

Might be something related to air suspension.

 

Oops, hopefully it will be here:

 

Figured it out! After an extensive look at the electrical manual wherein I just swiped through about 75 pages before I found a matching connector and picture it appears as though this is the mounting point for the lower accelerometer which is used by ACE equipped vehicles. As I do not have ACE the problem is solved! Hallelujah! Finally, an unplugged connector where nothing actually needs to be plugged in!