I have a manual t-case and the other day when I would pull it back into 4 HI could hear a click coming from a relay in the passenger side kickpanel. When I heard the click the light on the dash hadnt come on yet, becuase i wasnt moving, and so I figured the relay didnt turn the light on so it most likely is one that engages the ADD.
I opened up the panel and pulled out the relay... it took some testing but I found was I thought was the ground and I wired a switch into it. At first I had the wire sent over to the switch and then from the switch I grounded it to a nut by the steering column. Well that didnt work(there were blowing fuses and exlposions and fire coming from under the hood) and I guess it turns out the wire must not have exactly been a ground wire. The funny thing is I removed the relay opened it up and looked how every wire was cionnected and wrote down what I decided they were. I must have gotten the ground and the 12v activation wire mixed up.
So to make it work I undid the switch from the gounding nut I had set up and ran that wire back over to the wire I cut off the relay harness...
: If you want to use the relay in the cab to control the ADD it can be done. the end