When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Yep, has to do with your 4wd/ADD system. I'm not sure if it's actually needed to engage 4wd or not to be honest since when I swapped to a 5vz that plug was no longer used and just the vacuum lines were hooked up.
The wire is for the "4wd" light. If the vacuum lines are connected correctly, the wire isn't needed to engage 4wd, it's just to tell you if it engaged.