It's common on most Ford's for the light switch to burn out on most models. The newer vehicles have been fixed but that's where you could start.
In most vehicles flickering lights is a sign of a failing alternator.
My 2001 does that when the battery is drained and needing charging.
The battery group is 65N for a 2003 Ford Windstar
battery is low or almost dead
the same thing happens to mine........just turn the interior light switch of......it works
On a 2003 Ford Windstar : The cargo area is behind the rear seat
exactly where is of 02 oxigen sensor the ford windstar 2003
You must pull off the plastic panel from the inside of the truck to access the lights.
The 3.8 liter V6 engine in a 2003 Ford Windstar has a timing CHAIN
The last model year of the Ford Windstar was ( 2003 )
Lights on. Door wasn't closed all the way which left inside lights on
Make sure you have a good earth ground between the body of the car, the engine block and the battery.