The more I think about it, the more I think that you must have a
different switch/socket than the Projektzwo diagram assumes. The brown
wire shown is only to provide a ground for that exact lighted
switch/socket. If the switch from Ken is a generic on/off switch, DO NOT
CONNECT any part of it to ground. You do not need the brown wire at all
for the fog lights to work, only for the light inside the switch to come
on whenever the headlights are on so you can easily find the switch in
the dark. A different lighted switch may not use the brown wire either
or you may have the switch pins mixed up as it would not have the 83 +
83A pins labeled as such.

Ken, if you ARE selling a different switch and/or socket you need to use
a slightly different wiring diagram. Attaching the wires to the switch
for the customer would greatly reduce the chances of a mistake and
subsequent melt down. This Projektzwo wiring diagram is not obvious as
the relay is not controlled by the switch as most might assume, and as
is typically done in after market auto lighting. This diagram is for a
factory type installation which most home/auto electrical guys would not
be used to. This circuit has the relay controlled by the headlight
switch and the high current output of the relay directly connected to
the switch and then through a fuse to the fog lights. Not a typical way
to do things for the after market.

Mark