I have a 1998 ML and the dealer activated the internal fog lights a couple of months ago, but can't get the green light indicator in the dash to work. I've had the car back 2 times with information from the ML forums (ie: reference MB Net message #00138 and all that goes with it). They stand fast that "it's not possible for this model year". I don't know if they're not reading the information (not really trying) or if they actually tried and it's not possible on a '98. My next step is to contact the 'regional rep', but before that I thought I'd try here for feedback and confirmation that 00138 applies to a '98.

FYI - I talked with a service tech today at the dealer and he says that some of the early 98's don't have Option 11 (turns on the green dash indicator)in the AAM (as with my car). Funny though, Option 6 which turns the fogs on IS there. You think they would do it all or nothing, not half way(?).

Since all early AAM's had to be replaced due to programming problems & remote key failures, I would assume that your Truck has later version.