Around the year your trailer was built, there was a significant problem with the gears in the fuel pump being made of a phenolic material. It swelled when exposed to fuel and the gears would bind which caused the pump to stop working. Your problem may be related to those gears (then again maybe not). I'd first focus on the pump, make sure it's operational (or the cause of the problem) before branching out to other possibilities.
You can read a bit about the phenolic gear problem and some fixes here:
http://www.keystoneforums.com/forums...light=phenolic
There is a link if my post #4 in that thread that go to another thread that discusses the problem with swollen phenolic gears in great detail.