You can, but I'm not going to suggest you "jump" battery voltage to the PCM, in any case. That may not end well. The switch has several Batt+ outputs that power several systems. The switch isn't so expensive or difficult to replace to justify an extensive diagnostic, especially when it is a common point of failure. When it comes to the ign switch, it's best to eliminate everything else as best you can, then just replace it if that's what's indicated. If it hasn't been replaced, well, it's 20+ years old, and they often don't last that long. Even if it isn't the root problem, it's very likely due. If you can't locate a conductor, controller, or relay failure, the next step is a suspect PCM. The ign switch is the least expensive option at this time, by a long shot.