I use the enertia switch out of a 2000 and up Ford. the junkyards are full of them, just look in the trunk.
Enertia switches must be wired into the control side of the relay. They are not rated to handle pump current.
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.