Maybe someone can help me with this.. I have been fooling with the wipers for quite a while and strange things are happening. Originaly the wiper door would open but the wipers would not work. I tried various things finaly replacing the engine harness due to splicing and cutting my previous owners.
Upon doing this, the wipers would work but now the door will only open with the over-ride switch.
Now things get interesting. Coming home last night I opened the wiperdoor with the over-ride and turned on the wipers, the headlights blinked and the wipers did not work. Upon coming home I find out that the door now functions with the wiper switch again, but no wipers! Exactly the situation I had when I first started!
Anyone have any idea's
Thanks :confused:

 

Could this be a ground problem either at the switch or motor. I know i had to add a ground at the switch because the upper bezel was in 2 pieces.I know just how much fun the wiper system can be. :smash:

 

Terry, Thanks for the suggestion, I will see were that takes me.
Anybody else have a idea?
Thanks

 

I had fun trying to get this system to work right on my 71. Checking the grounds for the switch and the motor is a good start. The lid when it rises needs to push in the switch with a 'button' that's on the firewall. If this button switch doesn't work, no power will go to the wiper motor. And then there is the switch attached the back of the tachometer that allows vacuum to go to the wiper lid. Pretty complicated system!

 

Here is the text of an article on this subject from the old SHARK Quarterly files. This was a four page article, so it's a bit long. You'll want to print it out rather than reading on the screen. Hope it helps.

Save as: Wipers.001


Understanding Your Windshield Wiper Circuit
(non-pulse only)
by: Larry Ingram


One of those seldom understood parts of the 68-82 Corvette is its wiper system. This is particularly true of the 68-72 versions which had a unique door system interconnected to the electrical circuit. If the vacuum part of the door opening mechanism fails to open the door fully or the wipers don't park properly, then the whole set up becomes very difficult to get back into proper operation.

Since the Editor’s “Project “68" needs this work as part of the restoration, as well as the fact that the proper service manuals are hard to understand, I thought our readers might like to have the benefit of an “improved” repair guide.

Step one, as usual, will be to briefly describe each component as well as it's function. Then I will describe the entire circuit in the simplest language I can manage. I won’t be able to cover every detail but I will give you a solid grounding -- in more ways than one.

Wiper Switch - Most people expect the switch to be the power source but it isn't. It simply grounds the wiper motor and / or the washer pump. If the pump is wiper motor mounted it grounds a relay.

Wiper Motor - The motor is of a two-speed design using different field windings to produce the two speeds. Incorporated inside the gear reduction area of the motor is an electrical park relay and a small resistor. The relay serves multiple duties and can be the source of most of the electrical problems. Also as part of the motor (until about 77 or 78) was a mechanical washer pump driven on demand, by the driver, by the motor’s gear reduction unit.

Park Relay - The park relay, when energized, allows the motor to turn. It does this by simultaneously releasing its gear driven transmission and closing a set of points which are concealed within its plastic housing. (photo # 15 - optional as per space) This then allows battery power to the field windings; this power keeps it running. Internally, the motor has a field winding in series to its armature, as well as another winding called a shunt. The shunt when energized limits RPM, causing the slow speed mode of operation. The high speed current path is powered through the park relay’s points, through the field to the positive brush, and through the armature to the negative brush, from that brush to ground, via an internal circuit breaker. When the wiper switch is turned off the relay drops a hook (pawl) into the path of the rotating reduction gear, stalling the movement as well as pushing the points open to stop the motor.(photo #18) showing park pawl assembly) Observing the rotation of the shaft where the linkage is attached will show how the wiper arms get parked lower than in the normal sweep area. The shaft parks in an offset path relative to where it is rotating during normal operation. This is accomplished inside the gear mechanism by a slot that controls shaft position.

Limit Switch - Used only on 1968-72 cars this switch controls main power to the wiper motor, and is actuated by a linkage connected to the wiper door opening mechanism. The switch is open (off) until the wiper door opens to about 90% of its travel. Only if the wiper door is open should there be power to the motor on this circuit.

Override Switch (1968-72 only) - Placed under the dash below the steering column is a rotary switch as well as 2 vacuum switches. These switches allow servicing the related components, since the wipers will park and be hidden by the door even if the key is turned off, if not otherwise controlled by the override switches. Many a frustrated owner has had the experience of (apparently) failed wipers because someone turned the rotary switch to see what it operated. If the wipers were off at that time no response was noticed; but the first time wipers are demanded they won't work, if the switch was left open.

Electrical Control Relay (1969-72 only) - A relay mounted inside the console to the right of the radio, used to supply wiper switch information to the motor circuit. The relay is needed to allow parking of the wipers when the key is turned off.

Vacuum Circuit - 1968-72 cars featured a heavily advertised feature touting the missing or concealed wiper blades, actuated by a vacuum circuit. The vacuum circuit consisted of a large vacuum motor to open or close the door, a vacuum relay used to send vacuum to the motor, an override switch under the dash, an electrical solenoid behind the tach to send the vacuum signal to the relay and an interlock vacuum switch moved by the right hand wiper arm. Connecting all these parts are several feet of vacuum hose which can rot, be pinched, knocked off, or simply connected incorrectly. Problems tend to go un-noticed until the driver is caught in a downpour.

How Does This System Work

So, with these basic system components, the question now becomes, “How does this system work?”

I will begin by describing the operation of the wiper door system. The door is opened or closed on demand using engine vacuum, stored in a tank under the left fender beside the master cylinder. The tank is evacuated (supplied vacuum) by the running engine through a check valve and a filter. Vacuum is directed as two separate circuits to the vacuum relay: one operates the relay and one operates the vacuum motor (tank or double pie plate part mounted above the heater on the firewall, just to the left of the hood catch.) The relay is a spring loaded valve that can be pulled against the spring using vacuum on a diaphragm. This causes it to direct vacuum from the center port to one side of the vacuum motor while opening (ie: venting) the motor’s opposite side to atmosphere. Four hoses will attach to it, three large and one small one (it's signal). (photo # 22; use photo # 4) When there is no signal, engine vacuum is applied in at the large center nipple, routed internally to the nipple farthest from the diaphragm end and via a hose to the vacuum motor to open the wiper door via its linkage. When this happens the top nipple is vented to very bottom of the relay where there should be a foam filter in a square plastic framework. All of this is reversed if vacuum is sent through the signal hose to pull the diaphragm up; the valve pulls up opening the lower port to atmosphere and routing vacuum to the top nipple.

A vacuum signal is used to control the opening or closing of the wiper door. This signal is applied to the relay’s diaphragm to close the door, or the signal gets blocked off and the diaphragm is vented to atmosphere to open the wiper door. This job is done using a multiple switch path. The control circuit consists of three switches in series, the interlock valve under the wiper arm, the over-ride valve, and the solenoid valve. (photo # 20) This solenoid is wired to the wiper switch and therefore whenever the switch is turned on it is supplied a ground. The solenoid is live whenever the key is on receiving its power through the wiper fuse.

Here Is How It Works

Vacuum is applied to the vacuum relay diaphragm. Engine vacuum goes to the interlock valve via a hose. If it's depressed by the wiper arm, the vacuum continues via another hose to both the underdash over-ride switch and vacuum control solenoid. Either or both of these shut the vacuum off when activated, and simultaneously vent the vacuum that was in the diaphragm thus allowing the spring in the vacuum relay to switch vacuum to the opposite side of the vacuum motor and open the wiper door. Remember that the relay opens a vacuum path between two nipples and also vents the remaining nipple to atmosphere; it does not just switch vacuum only. When the wipers or the ignition is turned off, vacuum from the reserve tank will again be applied through the interlock valve, after the electrics park the arms, through the solenoid to the relay, unless the over-ride switch is pulled down. When the vacuum pulls the relay's diaphragm and piston up, it directs vacuum to the vacuum motor as well as venting the opposite side of the vacuum motor. It would be difficult to pull the motor diaphragm if the opposite side was sealed. Of course, if the override switch is pulled down the door will remain open as the vacuum path to the relay diaphragm is blocked.

By using vacuum valves in this way GM engineers were able to prevent changes in engine idle due to vacuum leakage below the carbs butterfly valves. If the hoses get reversed at a switch or valve, then whenever it gets activated a small vacuum leak is introduced and some change in idle should be noticed.

Now I Will Explain the Electrics

To begin, I will explain the basic set-up for the 1973 and later, and then add in the extras used in 1968-72. Even though these latter years had differences, there was a basic set of principles which applied.

As stated earlier, the wiper switch is only a ground source. The motor and washer pump are supplied power on a yellow wire that is fused by the wiper fuse & powered through the ignition key. If the key is on, then power is supplied to one side of the park relay (hidden inside the area covered by the washer pump or if the pump is under the jar then behind the cover over the gear drive). The other two terminals of the motor control circuit are wired as follows: terminal # 1 is used to create the high speed, while terminal # 3 controls slow speed as well as the parking command, when the wipers are switched off. These commands are received as follows, the wiper switch grounds both # 1 and # 3 for low speed and only # 1 for high speed. When the ground is provided the park relay magnetically pulls back the park pawl, allowing the motor to rotate the gear reduction unit. Simultaneously, a set of points inside the relay close allowing the power to the motor field, armature and brushes which are all in series to each other, with one brush being connected to ground via an internal circuit breaker. If the points fail to close, are burned or pitted, or a brush is worn down or simply hung up by rust or corrosion, then nothing happens other than the pawl moving. IMPORTANT NOTE: Because the wiper motor is mounted to a plastic body there is a ground wire attached to a terminal on the gear cover. This can also get knocked off, corroded or it's other end mis-installed. Whenever there is a problem begin by verifying the ground.

(Photo # 23 # 6 shows under dash override switch with pen pointing to “vent to atmosphere” hole which is only visible with the override switch pulled down in the “open” position - ie: to hold wiper door open)

1968 version - The circuit for 68 is unique and so far I have not found it in any service manual so this information was arrived at the hard way, 1 wire at a time on a car that had been messed with. The motor in 68 is not grounded conventionally. The ground brush is wired to the under dash rotary switch. This prevents using any other year motor without making internal changes. The park relay turns the motor on and off but the power to run the motor comes through the wiper door actuated limit switch (live at all times, fused at the horn relay by a fusible link ). This wire goes into the motor and attaches to one side of the park relay point set, through the points, field, brushes and armature and then back out of the motor into a harness that takes it to the rotary switch, the other side of which is grounded (switch closed). According to my notes there is a three-wire plug coming out of the motor, red is power, brown goes to the vacuum solenoid on the back of the tachometer (photo # 3 - optional for space), and a light blue which changes to a black going to one side of the limit switch, through the switch it changes to a brown, then to a brown with a white stripe, and ultimately goes to the rotary switch. Each of the color changes takes place at terminal plugs. Why it kept changing colors I don't know.

1969-72 version - To the best of my knowledge these years were all the same. In 1969, an inside console relay was added, as well as grounding the armature brush internally rather than via the rotary switch. The new circuit put the rotary switch in series with the door actuated limit switch. This means that power must flow through the switch and is easily checked with a test light at a connector going into the motor (heavy red wire). The wiper switch controlled the motor using the console mounted relay as follows. Energizing the relay switches motor control to the wiper switch, closing a set of points inside the relay case which grounds the motors # 3 terminal to cause low speed operation. If the wiper switch is moved to high then both # 1 and # 3 terminals are grounded causing high speed. When the wiper switch gets turned off, the relay looses it's power and the spring loaded point arm opens completing another ground circuit. This grounds the # 3 terminal allowing slow motor speed. Because the park relay lost its power when the wipers were turned off, it has dropped its hook out to stop the gear in the parked position, which (as it parks) will also open the field points within the park relay. This stops the motor. Ultimately the wiper door will close and disconnect the main feed by opening the contacts in the limit switch.

In this circuit set up the vacuum solenoid is wired in parallel to the relay. Whenever the relay is energized so is the solenoid. The control relay is wired, using 5 - 18 gauge wires, as follows:
- light blue, wired in parallel to the wiper motor # 1 terminal, the wiper switch high speed terminal, and the vacuum solenoid;
- yellow, wired in parallel to the wiper motor # 2 terminal, the vacuum solenoid, and the wiper fuse;
- light green, to the wiper motor # 3 terminal to provide the ground necessary for low speed operation;
- black, to the wiper switch for low speed, connected by the relay when energized;
- black /white stripe, to ground, this is connected to the light green if the relay is not energized.

The wiper switch used for all years has three terminals, # 1 grounds the washer pump when the switch is depressed, # 2 is for low speed, and # 3 for high. In actual fact both # 2 and # 3 are connected to ground for low speed. This translates to grounding # 1 and # 3 at the motor to get low, or # 1 for high. For the years 1968-76 the wiper switch receives its ground from the white metal dash cluster housing the gauges, later years had a proper ground wire. Note: Many of these housings have been broken by improper dash assembly causing intermittent operation. If your bezel is broken at the sides just above the gauge area I suggest that you add a ground wire directly to the switch. In some cases I, as well as others, have received a substantial shock touching here during troubleshooting. I guess the motor builds up like a coil looking for a path to ground.

So, that’s it. A rough guide to the whole wiper/wiper door issue. When I took on the assignment I thought I knew pretty well how the whole system worked. Once I started looking at the service manual, however, I realized how many important facts were left unstated and how badly the circuit diagrams of the day explained the situation. I suspect that a lot of other “guides” are equally poorly described, because this is a complex system. But how are you going to fix it, if you don’t know how it is supposed to work? If you want to add any important points from your experiences, I welcome your comments.

Parts for the repair and assembly of the wiper system on PROJECT ‘68 car were provided by Mid America Designs Inc. For more information on the many fine parts provided by that group, or for a copy of the Mid America catalog, contact Mid America Designs, One Mid America Place, PO Box 1368, Effingham, IL, 63401 or phone toll-free (800) 500-8388.

 

Wayne,
Wow.. thats some article, thanks, this will realy help.
Bob