My f350 1997 will not run on the rear tank . how do i go about finding what the problem is?

Well, first, to find out if its the in tank fuel pump or the tank selector valve, the cheapest and probable easiest thing to do is find the selector valve under the truck and switch the incoming fuel lines. front tank to rear tank inlet, and vice versa. If the truck still doesnt run, you either have an electrical delivery problem to the in tank fuel pump or a bad fuel pump. If after switching the lines, it does run, then you need a new selector valve

Well we know the switch valve,at the tanks is not working,but,is the manual control switch not sending the voltage to the tank?Without proper tools and,not being there to tell,the best way is to replace the manual control switch first.If this does not fix the problem,then the valve that switches the tanks,or the fuel pump in the rear tank is bad.A test light will tell you.When you switch the tank switch to the rear tank,does the fuel gauge change levels?If it does not change or drops all the way past empty,or goes past full,this tells us something.Past full tells us the switch valve is not working.If the level seams about right,then the fuel pump is bad in that tank.If the gauge drops past the empty,then the circuit is grounding out(wire problem).Take the test light and ground the clip to a good ground,and have the key turned on,and check the wires that are on the top of the tank.It should be a pink wirefor the gauge,it should light the test light,it might be dim(normal).If there is no voltage found there,then replace the switch valve.If the voltage is there,check the voltage to the pump(green or red).If voltage is found,then the fuel pump is bad.NOTE;THE FUEL PUMP RELAY PROVIDING VOLTAGE TO THE PUMP WILL CUT OFF IN SECONDS.The fuel pump relay only stays on shortley,unless the vehicle is running.I hope this was helpful.