2001 windstar o/d won't disable

My 2001 Winstar SE has a switch to disable overdrive. It no longer works. I tow my camper with this vehicle. Has anyone seen this problem and if so, where should I start? I have not dug into it yet but I will look into obvious things first (ie. fuses, connections). Any help will be appreciated.

My 2001 Winstar SE has a switch to disable overdrive. It no longer works. I tow my camper with this vehicle. Has anyone seen this problem and if so, where should I start? I have not dug into it yet but I will look into obvious things first (ie. fuses, connections). Any help will be appreciated.

My 99 has a pushbutton switch at the tip of the gear shift lever. First thing I would check is the operation of this switch.

My 99 has a pushbutton switch at the tip of the gear shift lever. First thing I would check is the operation of this switch.

I've checked the switch and it is ok. Would a burned out bulb in the dash cause the function to not work at all?