What is this wire?

[steviem]

Ok, i flushed my coolant again this morning, and sort of knocked this wire from its connection by water coming from the hose....

When I started the engine, it kept hitting the rocker cover and making a bit of smoke.

It looks like its supposed to be attached to the back right corner of the rocker cover and is black and brown.

[takethefifth]

Its an earth wire and should be reconnected asap!  There should be a connector about half way down the engine block if memory serves me correctly.....

[steviem]

For some reason it was connected to a bolt on the rocker cover?! I only started the engine, saw the smoke and thought, well I cant type what I thought, and turned the engine back off.

I'm gonna reconnect it, just need to get down to halfrauds for a ring connector (only bloody connectors I don't have!)

[takethefifth]

Not sure what engine yours is but on my 8v digi a small brown wire connects from the loom to a point about half way down and then on that rocker cover bolt that you mention i have a braided style earth strap going to my coil. 

[Haribo!]

im pretty sure its supposed to be on the rocker cover myself, it looks dead familiar

[Mr Blue]

looks like the earth for the clocks

[Breaker]

i had that wire on my 1.6 carb golf
it was on the front right rocker cover bolt and
is an earth. i remeber mine cause i didnt tighten it up
to well when i replaced it and the oil started leaking

[rubjonny]

It depends on the year of car too, my mates 89 GTI has both earth wires to the bolt holding the plastic coolant flange on, and my 90 GTI has one on the flange and the other on the rocker cover bolt.  There should however be a metal plate attched to the right rear bolt on the rocker cover, with a stud.  There should also be a braided earth lead running from the coil bracket to this plate.