it kinda sounds like the problem i had with the wipers on my tahoe [1997] my problem was some cracked solder joints on the circute board that is attached to the wiper motor assembly. if have & you know how to use a soldering iron, you can fix it for free. . below is what i cut&pasted from the alt. autos. 4x4. chevy-trucks newsgroup. hope it helps...
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-->Mid-90's Chevy and GMC Wiper Module Circuit Board
Replacement and/or Repair Procedures
The fault in this circuit board is quite common and is attributed to bad
solder joints from either design error or manufacturing flaw. Symptoms
which indicate a bad circuit board include (but are not limited to): wipers
will not work or work intermittently; wipers stop working for no apparent
reason, maybe even in mid-stroke; wiper function is erratic, with no delay
feature, delay is the same regardless of setting, or no low- or high-speed
setting; wipers may start to work if you tap on the wiper module or move the
electrical connector.
You have a choice of either Repairing your existing circuit board yourself,
or Replacing it.
Replacement - You have at least three options available to you, depending on
your relationship with your dealer and how much of a stink you want to put
up.
1. Pay for the replacement part plus the labor to have the dealer install it
(~$50 for the part plus ? for labor. Most expensive, least work).
2. Pay for the replacement part and install it yourself (~$50 for the part,
your labor is free. Takes about 15 minutes. ).
3. Have the part replaced under recall if applicable (Free, minus the time
your truck will be in the shop. Least expensive, most work. ).
4. (Repair it yourself - Instructions below after Replacement)
Option #1 is very straightforward, just go down to your local dealer and
have him do the work and pay the bill when he is finished. You don't even
have to read any further.
Option #2 is also very straightforward. Have the parts department research
the correct part number for your model year circuit board, purchase the part
from them and install it. The wiper module is a small 2"x 4" black box
attatched somewhere near the top of the firewall on the driver's side. It
has the wiper motor mounted to it, and an electrical connector plugged into
the end. Remove the electrical connector first, and using a Torx (6-pointed
star) driver, remove the cover from the module. The circuit board sits
directly underneath the cover and will be coated with grease. Gently pry
the circuit board out of the module, do a little spring cleaning inside the
case and add a dab of grease to the drive gears if needed. Install the new
circuit board in the same manner as the old one was. Clean the inside of
the cover and reinstall with the same Torx head screws.
Option #3 gets a little involved. First you must find a recall notice for
your truck. Start by checking on the internet at
www.nhtsa.gov and drill
down thru the links for recalls to determine if your truck is actually
listed (there are other sites to check as well). Just because your truck
may not be listed doesn't mean it's not under recall. It could easily
depend on how your truck is described. For example, a 1995 Chevrolet C1500
Pick-up could easily be listed as a C1500, 1500, 1500-3500, C-Series, C/K
Series, Chevrolet Truck, GM Truck, C10 (the old designation), etc. It would
pay to look under as many designations as you can think of before giving up.
If you find your truck as listed, so much the better. Print out a copy of
the recall and wave it at your dealer's service manager and they should fix
it No Questions Asked. If they still refuse, contact Chevrolet/GMC Customer
Assistance and/or the NHTSA's hotline (both are toll-free and listed on
their respective web sites).
If you do not find your truck specifically listed, all hope is not yet lost.
Search for the same truck under a different model year, or a substantially
similar vehicle which does have a recall (For example, the Chevy Blazer
shares the same wiper components as the Chevy S-10 and Astro, the GMC Jimmy,
Safari and Sonoma, the Olds Bravada, etc. ). Print out a copy of the recall
for the other vehicle and go to your dealer's parts department. Have them
search for the part number of the circuit board for the recalled vehicle,
then for the part number for your truck. Odds are in your favor that they
will both be exactly the same. Hence, your wiper module is one of the
faulty ones being recalled and should be covered but your truck may have
been left off the recall list. Take this info to the service manager and
depending on how much he wants to keep you as a customer, he will find a way
to have the board replaced under the recall. If not, then you still have
options #1 and #2 above, or you could fix your existing board yourself.
Repair - You can easily repair your existing board if you know how to turn a
screwdriver and know which end of a soldering gun to hold. If you haven't
mastered either of these skills, then have someone else do the job for you.
Step 1 - Locate the wiper module and remove the circuit board as described
in Option #2 above. Be VERY careful removing the circuit board. Do not
crack, bend or break it or you're outta luck and will have to buy a new one.
The circuit board is approx. 2"x 4" and has two distinct sides. The top is
the side where all the components live, especially the large black socket
for the electrical connector (more on that later). The bottom is where all
the lead wires from the electrical components poke thru the board and are
soldered to the printed circuit. Carefully wipe the excess grease off the
board.
Step 2 - The fault in the board is caused by bad solder joints holding the
large socket onto the printed circuit. If the board itself is cracked or
broken, then you will have to get a new one. Carefully inspect the tiny
mounds of solder underneath the large socket on the bottom of the board.
Each drop of solder connects a lead wire from the socket to the printed
circuit. A bad solder joint may look like it has a tiny circle in the drop
of solder around the wire end, a chip or crack in the little mound of
solder, or it may be too small to see. At this point you will need a
soldering gun and solder, and a steady hand.
Step 3 - Set your circuit board bottom side up so you can see the solder
joints for the socket onto the printed circuit. Heat up your soldering gun
and apply just a tiny drop of solder to the tip. Place the hot tip with the
melted solder directly onto the existing solder joint in question just long
enough until the gun melts the existing solder and the new solder mixes in
with it. Remove the gun from the work and allow to cool. Remelting the
original solder and adding some extra should repair the joint and make
continuity again and reinforce it. Repeat for all the solder joints in
question, and/or all the solder joints for the socket. Don't overheat your
work, or solder may run down and create a short to another circuit, or you
may unknowingly fry a component on the other side of the board.
Step 4 - Allow everything to cool, then reinstall the board as listed in
Option #2 above.
Attention: TDR Forum Junkies 
