if you buy an after market cruise control, chances are the OEM switch will not work.
rosta makes most of the after market cruise controls i believe.
they will supply you with a replacement arm that works with their cruise and fits in the multi-function switch (aka blinker/dimmer switch).
to remove the arm, push in hard, turn to disengage the lock and pull the arm out.
as far as the wiper/spray switch, i haven't figured out how to make it work...
my truck has an 89 astro column with all of the gm connections
i use everything but the wiper control
i also have a rosta cruise control, it is very nice