i was given a 86 pup 2.3 4x4 with a blown head gasket. i just replaced the gasket and all went well with that. the problem im having is the fuel pump. when i got it the pump was not hooked up to any lines. there are 4 branches coming off the pump. i think i got 3 of the 4. in on the rear, out infrontand the return on same side as out and just above the out. the 4th one is on the very top of pump comming out horizonal thenbends 90deg pointing downward. what is that one for?