[Dkennel]

how about this:
The following was provided by Jason Savage (jsavage@crystal.cirrus.com).
Intermittent Wipers
Problem:
'89 Carrera (not a C2 or C4) with intermittent wiper dial. Up until the failure, the intermittent wipers worked fine, and the wipers would park in the correct position regardless of when you turned the intermittent wipers off. The continuous wipers also worked fine, and would park in the correct position even if you turned the wipers off in the middle of a wipe. During my drive to work in a light drizzle one morning, the intermittent wipers had been on for about 30 minutes and were working fine, when all of a sudden they switched into continuous wiping mode. When I turned the intermittent dial off, the wipers would stop wherever they were at, and would not return to the park position. I also noticed that the continuous wiper mode also lost its ability to park the wipers properly. In order to have an unobstructed view when the wipers were off, I would have to time when I turned them off so that the blades were somewhat near the park position.

Solution:
NOTE: SPECIAL THANKS GOES OUT TO CHRIS BENNET FOR THIS SECTION. THE MAJORITY OF THE INSTRUCTIONS BELOW ARE HIS, WITH A FEW COMMENTS OF MINE ADDED IN.

Tools: 7mm, 8mm, and 10mm socket, socket driver, 10 mm wrench, phillips screwdriver, flat head screwdriver (for prying relay open).

Getting in there:
Removing the hoses and air box is very easy. Review the following instructions before starting, and you will be at the relay in less than an hour, even if you go really slow. There is no difficulty in performing this job yourself - the second time you have to do it (hopefully on someone else's car), you can get to the relay in 10 minutes or less. Here is the tricky part - the fresh air box is fastened to the car via two "hidden" screws located under the black screen for the fresh air inlet (see STEP 5). If you face the windshield (while standing outside the car with the trunk closed) and look behind the black screen, you can already spot the two screws.

Here are some highlights of the disassembly:
NOTE: All directions are relative to sitting in the trunk, facing the windshield.

STEP 1:
I used a socket driver to remove (most) of the hose clamps (7mm). I ended up completely removing the 2 hoses on the left side, and the one closest to me on the right side, i.e. the one connected to the right side of the blower motor.

STEP 2:
The plastic "Y" shaped hose joint (in the center of the car, just below the blower motor) that goes into the floor of the trunk of the car is held in place by a phillips head screw that you can see - the back of that "Y" shaped hose joint is just held down by a clip that it slides under. I.E. Unscrew the little screw connecting joint to floor and pull the joint toward you. Stuff a rag in the hole so you don't loose something down there. The hose connected to the right side of this "Y" shaped hose joint is pretty long, and can remain attached to it during your work. Just move the joint/hose to the right and out of your way.

STEP 3:
To get that brace on the right out of the way you have 2 options: 1 - remove the vacuum hose blocking the bottom bolt, then loosen the bolt (10mm) about a 1/2 turn. 2 - using a 10mm wrench, squeeze the wrench in between the vacuum hose and loosen the bolt about a 1/2 turn. By loosening the bottom bolt on the brace, you can remove the brace's top bolt (10mm) and swing the brace out of the way.

STEP 4:
Remove the top half of the blower assembly (2 screws, 8mm), unplug the blower and swing the top half of the blower assembly out of the way. You can't remove it completely out of the way because it has a control cable attached to it.

STEP 5:
Remove the cover that holds down the black screen that covers the fresh air inlet (4 phillips head screws). Once the cover and black screen are removed, you can now get to those two top ("hidden") screws and pull the plastic blower assembly down. The assembly may still seem fastened to your car, depending on how long it has been sitting in there. Here is why: There is a rubber (grommet?) along the perimeter of the assembly where it is pushed into the area nearest the air inlet is (i.e. the area where the black screen used to be). You are basically breaking that n-year old seal. The trick is to wiggle/push on the assembly with a force that is in the same direction as the two "hidden" screws you just loosened. It helps to first disconnect the drain pipe located at the bottom of the assembly before applying any force, so that you are not working against the drain pipe.

STEP 6:
Once the plastic blower assembly is out of your way, you can see the intermittent wiper relay. It is part #911.618.149.01 for model years '76-'89, and part #911.618.149.00 for '74-'75 models. In my car, it is just to the right of a blue, slightly larger module that is part of the factory alarm system. If this is the same thing you see in your car, here's another trick: there is a section of the wiring harness running between the alarm module and the intermittent wiper relay. You have to pull up this harness slightly to get to the nut beneath it that fastens both modules to the firewall. Once this nut is off, you can get the relay module out of the car out by unplugging it from its connector.

STEP 7:
With the relay out, pry it out of its case by using a flat head screwdriver. The contents of the relay module slide out on a little printed circuit board, and all you have to do is clean the relay contacts by gently sliding some 150grit (or finer) sandpaper in between them. I also sprayed some contact cleaner in there (the stuff Radio Shack sells for $7.99 for cleaning up stereo volume knobs, tv dials, etc). This stuff does not evaporate easily, so I spent some time wiping excess contact cleaner off the rest of the circuit.

Before reinstalling the relay, I performed some testing per Chris's request:
I. With the relay out of the car, I turned on the continuous wipers. They will turn on, but still will not return to the park position when you turn them off.
II. As expected, nothing happens when you turn on the intermittent wiper dial.
After reinstalling the relay, but before putting the fresh air system back together, I observed the following:
I. Everything works: intermittent wipers, continuous wipers, and park functionality.

STEP 8: To quote the Hayne's manual, "reinstallation is the reverse of removal," but please learn from my mistake: don't forget to reconnect the drain pipe (mentioned at the bottom of STEP 5) to the plastic blower assembly before you focus your efforts on getting the blower/rubber grommet positioned back into the car.