6mm allen key, little brass plug, drain it and hopefully the light goes out.
The sensors are fairly common to mess up and stay on or false triggers, and the plug can be a PITA.
If the plug is fighting you are stripping out, Ford/IH have an improved plug that came on the LCF trucks.
Ford part number: 6E7Z-9C082-A
International part number: 2589259C91
List price is around $16.00
Part numbers from this article,
http://www.forddoctorsdts.com/articles/article-05-19.php
On my truck I ended up having to remove the pump from the truck and pull the cover off so the plug could be drilled out and replaced. That was at around 80k and the previous owner never drained it.