gas tank wont switch from back to front

My first rig was a 1981 Ford F150 with Dual Tanks, man I loved that thing, but gas was 99 cents a gallon back then... if the switch is not occurring it could be two things, the switch in the dash, or the switch at the tank. Pull from a junkyard and start there. The other thing is that both tanks are fitted with separate filters, but only one pump, so if one tank is working and the switches have been checked (and aren't malfunctioning) it may be a filter on the 2nd tank. Let me know how this turns out! I will monitor your post! Best of luck!

ok if i turn the key on i can hear the pump when its on the back but not the front

Then I would think its the filter. If you know the switch is good, (which if you flip it while the first tank has gas in it, and the truck starts sputtering out), you know the switch is good in the dash. Now testing the switch in the back, at the tank is more difficult but I would slap a new filter in it.