You all really need to read the factory service manual and look at the factory wiring diagram.
1) There is no inertia switch on an 87 Chevy truck
2) There is only one oil pressure switch that controls the fuel pump. Again, this is used once the engine is running and there is oil pressure.
3) The relay is only used to prime the system prior to oil pressure rising. The relay is controlled by the computer and is only activated for about two seconds after turning the key to START. Yes, as I noted above, a good troubleshooting method is to remove the relay (which is on the firewall) and jumper across the pump terminals to get the pump to stay on.
4) The only other switch in the fuel pump circuit (other than the ignition switch) is the tank selector switch if the truck has dual tanks. That's it. This is a very simply circuit.
By the way, if the relay (or computer activation of the relay) goes bad, it is often possible to start a TBI truck by cranking the engine long enough to build oil pressure. That will finally turn on the pump and operate the TBI. This can take quite a while.