I wrote:
>red/yellow and brown for '90 -- obviously the brown is ground in
>each case.  But how they're connected to the sensor

For what it's worth, on my '89, if you look into the end of the
harness plug (mine's black) with the spring on top; the ground
(brown) is on the right and the +12 on the left.  Sensor lead is
separate, female fast-on with boot that connects to the likewise
booted female fast-on on the harness with a double-male adapter that
fits the boots.

Yours,
David