That sounds exactly like the swap I done on my '84 last year. You'll need to swap the entire wiring harness out of the runner. The '89 harness will work with your '84 gauges. All I had to do was put a bulb in my '84 panel where the check engine light is. It has the place for it just no bulb. My tach , oil pressure and voltage gauges worked fine. The only modification I did to the '89 runner harness was to remove all the wiring that runs to the center console for the rear window stuff , everything else went great. Another thing you'll want to do is make sure you get the clutch start cancel button out of the runner or just wire the 2 wires together on the plug. Otherwise you'll be wondering why you can't get it to turn over like I did.
