anyone use a fuel pump kill switch?

[55 Rescue Dog]

True, just another wire won't do it. Since GM uses oil pressure as part of the fuel pump circuit it might be a little more involved, unless there is a 12 volt relay somewhere, sending power to the pump. The simplest way would be to just put the inertial switch in series directly to power the pump if it is capable of carrying the current of around 10 amps. That's the way Ford did it on a lot of vehicles, using the 3rd terminal to turn on a dash indicator light. It shouldn't see any duty cycle, which a relay would need to do every time you powered it up. I have had to troubleshoot many intermittent electrical problems that ended up being caused by a bad relay contact. Much easier with only a switch in the way. It was pretty easy to troubleshoot a relay on a machine tool back when you could check relay contacts by manually operating a relay by pushing it in with a screwdriver to check contact resistance. Too bad cars were not designed that way.