i can tell you what happened on my 88 when that happened: the air
filter box was incorrectly repositioned. yup. it seems that the
fuel injector wires on that side of the engine can get pinched
between the air filter box (the black plastic big box) and the
little metal shelf (into which the air filter box sticks its
little feet) ... after a few days/weeks of vibrating, the
insulation on the power wires to the injectors are worn away, and
short out to the metal of the chassis (the shelf).

when this happens, the injector power relay overloads and the
whole harness melts down. :( it was $1200 to replace the brain,
idle stabilizer, relays, harness ... all with used junkyard
parts. :(

and it's possible that the catalytic converter glowing was a
result of the leaned condition of the injector wiring melting.
maybe.

so everybody whose harness has NOT melted (not so fast there,
Daniel!), get out there and check those injector wires on the
right/passenger side of the bus ... under the air filter box.
make sure they are not pinched by that shelf.

as a note, it seems that vw was aware of this problem ... the 90
and 91 models came with the wires cable-tied out of harm's way.
:(

joel