I have followed some of the recent comments on the generic three wire O2
sensor. In my case, when I converted my '82 Diesel Westphalia to a '90 1.8 L
8V GTI Digifant engine, I had the privilege of building the wiring harness by
melding the diesel harness with that from the GTI. The original O2 sensor was
replaced with a generic from Ford (Mustang, 86, V8) since that was the
cheapest available. More recently I purchased a generic from Bus Depot (Bosch
number 0 258 003 913, which also has the sub-number 13 913 on the box). I
noticed at once that the two units were identical down to the details of the
electrical connector. In my installation, I picked up a female connector from
a Ford product (I got one from a Thunderbird, but all the V6 and V8 three
wire connectors I ran into on FOMOCO products were the same - 84 to 92), got
the VW connector end from a crushed sensor (lots of these in the yards) and
soldered up an adaptor cable. As Darrell says, use a high temperature version
of a shrink wrap tubing for insulation. I also used the high temp silica
sheath from the FOMOCO units as a secondary thermal insulation. I
contemplated using a braided ground shield, but checked several factory
installations and found none, even though the total run length was more than
that required for my conversion. Works fine. I checked for pickup noise on
the line at the firewall connector with a scope and found nothing.

Now I'm prepared for an inexpensive swap-out whenever the sensor goes south.
Actually, I have swapped sensors several times for diagnostics when
troubleshooting. The Ford connector is easily the quality of the VW original.

Frank Grunthaner