2004 Toyota Highlander | Stereo Wiring Diagram 2004 Toyota Highlander. October 6th, 2012 Posted in Toyota Highlander. 2004 Toyota Highlander Stereo Wiring Information. Radio Constant 12V+ Wire: Blue/Black The stereo wiring diagram listed above is provided “as is” without any kind of warranty. Use of the information above is at your own risk. Leave a Reply. Name (required) 2004 Toyota Highlander OE Wiring Harnesses & Stereo Toyota Highlander 2004, Aftermarket Radio Wiring Harness by Metra®, with OEM Plug. For aftermarket stereo. Metra preassembled wiring harnesses can make your car stereo installation seamless, or at least a lot simpler.