Okay let me see if I am understanding correctly: The issue is that you do not know where the red wire coming from your switch goes to?
If that is the case, wire it to your fuse box (drivers side under the dash) using an Add-A-Fuse in the WIP (Wipers) fuse slot (use like a 5amp fuse). This only has power when the key is in the ignition or when the engine is running. This will give your switch LED's power and allow your switch (when enabled) to give the OK for your relay to draw power from your battery.
You can buy an Add-A-Fuse from any auto store for like $3.99. I bet if you brought in your harness that they would even crimp it for you if you asked.
FYI, for 5th gens you'll need the MINI Add-A-Fuse. To be specific, this is what you need:
Advance Auto Parts - Down for Maintenance
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Smeerun's Build Log] - 2016 4Runner Trail Premium MGM w/KDSS
Exterior: Toyo OC A/T III 265/70/17 (TE Wheels) | Dobinsons UCA's + C59-302/GS59-700 Front + C59-500/GS59-705 Rear | C4 Rock Sliders | SSO Roof Rack | Ironman 8.5" Awning | Tacoma Low-Profile Antenna | Diode Dynamics SS3 Pro Fogs | CTH Folding Mirrors + LED Sequential Blinker Mirrors
Interior: VanTrue N4 3-chan Dashcam | Husky Liners Floor Mats | Canvasback Rear Covers | Blue Ridge "Attic"