I'm still laughing from that wiring diagram. Looks like a lot of home-built cars out there.....
I had a heavy wheel vibration for years across two different sets of tires (Continentals and Michelins ) in the 65 - 70mph range (16" wheels) until I finally had my current set "Road Force Balanced" at a car dealer's shop. That made a huge difference and now the vibration is pretty much gone. IIRC, the cost was under $20 USD per wheel.