Ford Repair: electrical problem with towing package, lamp bulbs, turn signals

Question
I have a 98 Expedition that I have been towing my boat with for five years and no problem until now.
The turn signals and the brake lights work fine but
when I turn on my running lights or headlights it blows the fuse for the trailer lights under the hood.  I connected another vehicle to the trailer and everything works fine. Do you think its the light switch?

Answer
Hello and thanks for the question...I'll try to help.
With the trailer not connected does the fues still blow? If it does, I would look at the head lamp bulbs....remove them and then turn the lights on..see if the fuse blows. If it doesn't..replace the bulbs. If it does....take a look in to the switch.
Erik