Ford starters are pretty basic. Ignition switch, solenoid, starter. Need to ask a couple questions to help zero in on the problem.
First make sure the "house" power is off so you are only using the chassis wiring.
Next, as Jamie asked, any clicking sound when turning the key to the start position?
Do the dash lights come on with the key as usual?
With headlights on, do they dim when the key is turned to the start position?
What exactly was the part that you and your friend replaced?
Do you have access to a 12v test light?
Sorry to play 20 questions but I don't want to send you in the wrong direction.
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