In order to install a trailer brake controller like the Hopkins Agility # HM47294 that you referenced on your 1989 International S1900, you will need to first install an RV style 7-Way connector if one is not already present.
I recommend starting with a 4-Way harness like the Tekonsha Universal 4-Pole Hardwire Kit # 18252. This kit includes a tester that will allow you to determine the correct wires on your truck to splice into.
Once installed, you will need the Universal Wiring Kit... view full answer...
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