Yes. You just use the small wire going to either the starter or the solenoid on the fenderwell. Not sure how the 91's are configured.
In older Fords, the relay (sometimes also called the external solenoid) was on the fenderwell. In newer s it's integrated into the starter.
If there is only a large gauge wire going to your starter, then the control relay is on the fenderwell just aft of the battery. You'll see the big wire from the battery going back to the solenoid, and a big wire coming out of it going to the starter. There will be one or two small wires also going to the solenoid. You can pull one of them off and see if it works and then that's the one you interrupt.
If there's a small wire going to the starter and no external solenoid, then that's the wire you interrupt.
The solenoid coil draws up to 10 amps or so though depending on the design, so you need a half decent switch or relay. Most I think draw much less, but that's a good design goal I think.
Hope that was clear.
Sadly, when you use a username like that you'll get ignored by a large number of posters here -- but that's "normal", lol. There's more than a few serious Christians on here though, so don't let it push your buttons.
In fact, some WILL try to push your buttons and beware of the "Religious and Political Discussions" forum unless you're very good at apologetics, lol. It's like the wild west over there sometimes. My Christianity is well known here and though some want to play games, most are tolerant.
But anyway welcome, be blessed, and lift up the name of Jesus!