Classic 'run-on' from making the changeover. The large 0/1 AWG wire should be run from the HOT side of the selenoid (same side as the battery lead) to the large post on the starter. A smaller 16 AWG wire should be made up to run from the switched side of the selenoid (where the large starter wire used to be) to the small post of the starter. This smaller wire could alternately be run to the ignition post (small post) on the switched side of the selenoid. Just make sure that NOWHERE along the wiring do the two wires have a possibility of contacting each other, like at the starter posts, or you'll have continued run-on.
BTW: Switching from the pre-93 starters to the 93-up starter is a good idea. Its a higher torque starter and it weighs about 7 pounds less than the pre-93 monster that came on the 5.0's.
I've got this change in my Tech Tips section on my website.
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Jeff Chambers
Trophy Stock #3
11.611 Seconds / 116.98 MPH
Chambers Racing Team