I have not been able to find a suitable wire in the back of the Headlight switch and dash variable light intensity reostat to hook up a light in my new Autometer boost gauge. I have a wiring diagam from a Haynes manual, but the wire colors do not match what I have?? I have a 2003 Tahoe Z71. Any Ideas on where I can get the power for my boost gauge light that works with the dash lights? Thanks.