It's actually a product that can be purchased to load/unload your boat from your truck:
http://www.trailersystems.com/index.htm
However, I still feel that teh F150 is overloaded......my opinion of course.
Boat and trailer...probably in the 3000 lbs area (perhaps more, I'm not a boat person so I really don't know). All that in the back on a F150, definitely not safe.
I'm currently towing a 27ft travel trailer, but hoping to get into a fifth wheel soon (hence the truck in my sig).
Truck pictured was my '02 YukonXL. I'll have to make a point to take a new picture this spring.
On my trailer, the brake light and signal lights, although the same bulb, it actually a double filament bulb. Thus, your brake light can be out, but not the signal light.
I would try changing the bulb and see what happens.