They are wired in series with the power wire in every one I have ever seen. That is one thing I like about fords ,It makes it nice to hook a scope up to and check out the fuel pump on the feed wire.
You are correct about the Fords wiring the enertia switch into the pump power wire. What I should have said was some after market fuel pumps pull more current than a stock Ford and I've never known what the max current rating is for the switch, so I wire them into the control side.