earth points

[V8CER]

having problems with the Tacho it dies when I apply the brakes and is unreadable at high rpm.have replaced the big fuse and holder then fitted midi fuse to no avail. Have agitated all the red power leads around the engine with no effect and have substituted new earths to chassis and engine direct from battery still have the problem does anyone know where the ecu has its earth point and any others around the instrument looms?

RGDs peter