A couple people have asked about my use of the X signal from the
ignition switch for battery relay control. This is an alternative to use
of the alternator blue wire as done by VW. Most times it is people with
engine conversions who desire a different control signal since some
alternators have trouble doing this job.

For all years this X signal is available at the back of the rear window
defogger switch. Look for the black/white wire there. This wire has
fused power whenever the key is turned on, except during starting.

86-91 models also have other places that are better but the exact
details vary depending on installed options. In general the back of the
fuse panel has G1 and/or G3 available to plug in to for X power. Some
owners can  just move a blue wire from G4 over to either G1 or G3, or to
an open yellow/black wire stub hanging from one of the two. This
switches an existing fridge or aux battery relay over to X signal
control. G1 and G3 are powered by fuse S12, which also powers other
options as fitted.

Mark