'87 944 n.a. -- been monitoring the fan behavior (etc.) from summer,
cold winter, to spring (now, warm).  my question is essentially about
which suspect failed (or 'partially' failed?) part needs replacement :
sensor or sender or relay  ("or", as in a Venn diagram : sensor V
sender V relay)?

i _could_ replace or test everything, and i _could_ replace one-part-
at-a-time
(starting w/ the relay), but it'd be more interesting to do better ; i
reviewed clarks-garage cool-01.htm late-model 944's w/ AC, but, i
would be interested to know if a single bad part be inferred from the
following scenario -- if not, is the relay the first thing to test/
replace?

scenario : at best, the radiator fans turn on and cool the radiator,
at worst they can stay on until the battery is drained.  slow/fast
speeds are apparently attained OK.  there seems to be a correlation w/
cold weather and wet conditions at the same time.  sometimes, there is
a trend w/ ignition stage (i.e. turn the
key one 'step', or 'two' with 'three' activating the starter).  fans
can turn off when temperature is low enough w/ key out.  these things
seem to change w/ outdoor temp.  A.C. button seems to start fans.  as
an aside : radiator seems to leak w/ pure antifreeze and cold weather,
but seems much less w/ warm weather and approx 1:1 diluted antifreeze.

thanks for reading.

-bryan