Rocker head earth wire

Hi
Mk1 GTI  cabriolet 1989
I have an earth from my rocker cover to the coil…that's fine. There is also a brown white wire attached to the rocker cover. my question is where does this brownwhite wire go to??
I hope this will sort my lack of rev counter. I got another set of clocks thinking my problem would be solved ..but no. so please help me. Thank you

See your other thread in the HELP section.

Brown wire on my rocker cover earths the instrument display, without it the clocks have a mind of their own when the lights switch on.