How does the starter motor earth?

[Robb]

Just wondering if the starter motor is supposed to have an earth wire? Or does it earth itself through the engine?

My starter is very slow when my engine is warm (most of the time it is slow to start othertimes it wont start at all and just sounds like the battery is completely dead!), i suspect this could be an earthing problem.

I took a look at the starter motor this evening, but could only see 2 positive cables so I am assuming the starter earth via the engine?

Looked at my engine earth, but this seemed in good condition, so I couldnt really find a fault there?

Any help anyone may have would be much appreciated

[maxfax]

The starter earths itself though the engine block, well more precisely the transmission..  Do a voltage drop test on the earth wire from the battery to the trans...  It can look fine but not be, and they do tend to be troublesome on these cars..  If the earth checks out okay do a voltage drop test on the positive cable between the battery and starter..  IF nothing still shows up chances are it's the starter itself... 

For a "how to" on the voltage drop test read this http://www.vwdiesel.net/forum/index.php?topic=22321.0

[Mark(The Miser)UK]

Clean the mating surfaces. The mk 2 Passat has additional earthing through a support bracket at  the other end.This is sometimes missing! Not sure about the transverse setup.
Over a period of time the starter gets dripped upon with oil from the cam cover gasket leaks/filler cap drips.
Clean and dry internally too!

[Wayland]

Make sure your starter bolts are tight.

[RustyCaddy]

You can also ground the starter housing with a wire attached to one of the screws at the back (battery side) of the housing on a MK1 style starter and run the other end directly to the battery ground post as a temporary fix...in my case it has been a temporary fix since '07