87 R10 Fuel Pump not Priming
 

My grandad gave me his 87 truck and when I turn the key on the fuel pump does not prime. The last thing he did to the truck before he died was put 2 new pumps in, all to find out it was the switch in the dash for the left/right tank that had fouled out. This was 2 years ago. I have checked the fuses. I can't get it to get fuel so the truck is just sitting and I can't let it just rot. There isn't a spot of rust on it.
what should i check? The electrical is much more complicated than my 71, so I dont really even know where to start.
thanks