Not sure about the '91, but 92 - 95 has an ICU, or Integrated Control
Unit plugged in at the back side of the under-dash fuse box. This unit
has the intermittent wiper circuit, the seat belt reminder chime etc.
Now, I don't know if the lesser trim levels use a different ICU, or if
the intermittent wiper circuit is present on all trim levels. I do not
know if the '91 is similar to the 92 - 95.

As randolph says, you need the
correct ICU. I think, based on
my study of the diagrams to
build my own intermittent
wiper control, that 88, 90 and
91 Civic and CRX ICUs will work.
I could never find one in a junk yard.

As to buying an after market, or
rolling your own, I would have to advis
against that course. It took me about 2
months to get mine debuged.
Good luck on finding a ICU.
Terry

you need the underdash unit...........not fun to change!!!!!!!!