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Fixing The Main Wiper Switch

INTRODUCTION

This document describes how to fix the wiper switch. I have done it on my '87 RX-7 (turbo, tilted steering wheel) and it cured the problem. The symptoms were that the windshield wiper works only in LO speed but not in INT and HI positions. This document describes how I performed the fix based on directions posted by several people in the FC3S list. It is up to you to decide if this fix is appropriate to your case.

FORWARD

The wiper switch controls the main windshield wipers as well as controls the rear window wiper, misters, and hazard lights. The wiper switch seems to have a problem common to many 2nd gen. RX-7's. In my case, the main windshield wiper did not work in the HI and INT but works just fine in the LO setting. New wiper switch units are available from Mazda dealers and Mazdatrix; but due to their high cost (over $200) some RX-7 owners might choose to fix them instead. The problem in my case, as pointed out by people on the FC3S list, was bad contacts in one of the relays. The FC3S FAQ suggests to clean the relay switches; however some individuals on the list mentioned that this fix is only temporary. In so being, I decided to replace the damaged relay with a new one. The relay I used, as suggested by Mike Gordon, is G6C-2114-US-DC12 made by Omron Electronics Inc. This is a 12V, PCB relay, 8A SPST-NO/SPST-NC which is a drop-in replacement and its pin-out is identical to that of the original relay. A good source for the relay is Digi-Key (1-800-344-4539) which carries this relay as item Z950-ND. It can be ordered using Digi-Key's on-line ordering system and it costs $6.24 plus a $5 penalty for small orders plus the actual shipping cost.

The main difficulty in performing this fix is to access and remove the old relay. The FC3S FAQ suggests to remove the wiper switch printed circuit board (PCB) by de-soldering it. Another approach which was suggested on the FC3S list is to cut, using a Dremel tool an opening in the wiper switch cover; this is the method which is described in this document.

The rest of this document describes how to replace the faulty relay with the new one. It also contains a sections which describes how to verify that the relay in your wiper switch is indeed bad.

REMOVING THE WIPER SWITCH AND ITS COVER

Removing the wiper switch and its back cover are done in the steps outlined below. When done, you will end up with the 'naked' wiper switch as shown in Figure 1.

Figure 1 - The wiper switch taken apart.

Note that the instruction below are for an FC3S with tilted steering wheel which might make the removal of the wiper switch easier. If your car does not have a tilted steering wheel, follow the instruction in the Shop Manual to remove the unit.

Disconnect the NEGATIVE battery cable (with negative ground cars like our FC3S, always disconnect the negative cable first and connect it last, this reduces the risk of causing short circuit by touching the car body with the wrench).

Note: the switches should be plugged in and out only when the battery is disconnected and the ignition switch is off. We will not mention it again in the rest of the document so it is your responsibility to remember that.

Remove the cluster switch panel (the unit that contains the wiper, signal, light, and cruise control switches). Note that the cluster switch panel is held in place by five screws (2 at the bottom and 3 near the instrument panel) and is connected by four (in my FC3S which has cruise control) electrical connectors (two at the right and two at the left).

Remove the wiper switch buttons. This is done by holding them firmly and pulling them away. You may also push them with a screwdriver from the inside of the cluster switch panel while you pull them away.

Remove the wiper switch. It is held in place by two screws. In my case, I had to remove also the cruise control switch to clear the way for the wiper switch.

Remove the wiper switch cover, this is done by prying on it with a screwdriver. Be careful not to damage electronic parts under the cover. The cover does not seem to break easily and even if it is breaks, it is not a big problem as you can glue it back without affecting the performance of the switch.

If everything went OK, you will end up with the parts as shown above in Figure 1.

CHECKING THE RELAY

Before you replace the relay, you might want to make sure this is indeed the cause of the problem. First you need to identify the relay. The wiper switch has three relays: Relay 1, Relay 2, and Relay 3. The three relays are mounted on the component side of the PCB. Relay 1 is fully exposed, Relay 2 is partially exposed, and Relay 3 is fully covered. Figure 3 shows the three relays after exposing relay 3 (more about it later). Relay 3, which is the one we are going to replace, is shown on the lower right corner in Figure 3 (this relay is the bottom relay when the WSC is installed in the car).

Now we need to identify the six pins of Relay 3 on the back side of the PCB. The six pins, which are directly below Relay 3 has the following pin out diagram:

Figure 2 - Relay 3 pin out (bottom view). Contacts are shown in the normal (rest) position.

Before we start with the check, note that this is a brief check that tests only for the common symptoms of malfunction, that is, that one of the switches of the relay does not connect when it should. It is also assumed that you are using a digital voltmeter with automatic polarity setting. If not, no problem, if the voltage you measure is negative, exchange the position of the two probes.

Relay 3 contact check:

With the battery disconnected, connect the wiper switch to the car (we don't need the other switches at this point).

Make sure nothing is going to short circuit, and then connect the battery and turn the ignition switch to the ON position.

Set the speed to LO and make sure the voltage between the pins of the relay coils are close to zero VDC.

Measure the voltage across the normally closed contacts of the relay (upper left corner in Figure 2). It should be zero VDC since the relay is not activated.

Set the speed to HI and make sure the voltage between the pins of the relay coils are about 12VDC.

Measure the voltage across the normally open contacts of the relay (lower left corner in Figure 2). It should be zero VDC since the relay is activated.

If one of the switches has 12VDC across it while it should be closed, the switch seems to fail and replacing the relay is likely to fix the problem. Otherwise, further investigation which is outside the scope of this document is required. In my case, the normally open switch failed to close.

REMOVING THE RELAY

To remove Relay 3 you need to access the relay from both sides of the PCB. The removal of the switch cover done earlier has exposed the PCB side of the relay. Now we will need to expose it from the component side. Figure 2 and Figure 3 (a close-up) show the component side of the wiper switch with the relay exposed. Using a Dremel tool carefully cut the cover until Relay 3 is fully exposed.

Figure 3- The three relays from left to right are Relay 1, Relay 2, and Relay 3. Relay 3 (right) being the one we are going to replace and is is exposed from the component side by cutting the switch surface.

Figure 4 - close up of the exposed Relay 3 (vertical, on the right hand)

After exposing the relay, remove it by de-soldering its six pins shown in Figure 5, and puling it out. It is hard to pull the relay out intact but don't worry if you damage or break it, as we are going to replace it anyway. Be careful however not to damage the PCB or other parts of the switch. I found that it is easier to remove the relay if you can access it with a screw driver from the side, between its base and the PCB. For that reason, I made an extra hole on the right side (using the orientation in figure 3) of the switch as shown in Figure 5.

Figure 5 - the bottom side of Relay 3. Note also see leverage access hole marked 'H'.
If every thing went OK, the PCB at the vacant location of the relay will look as in Figure 6. Make sure to clean any excess solder that can shorten between PCB traces.

Figure 6 - A close-up of the vacant location of the Relay 3.

INSTALLING THE NEW RELAY

To install the new relay in place of Relay 3, simply make sure that the PCB and the six holes of the relay pads are clean (look for short circuits on the component side under the relay, after installing the relay, you will have not access to clean it), insert the relay and solder it carefully. Note that because of the asymmetric spacing between the relay pads, it fits in only in the correct orientation. The installed relay is shown in Figure 7.

Figure 7 - The new relay installed in the vacant location of the Relay 3. TESTING THE SWITCH

To test the switch you don't have to install the entire cluster switch panel. You can simply connect only the wiper switch itself, and test it separately. Make sure that when you connect or disconnect the wiper switch, the battery is disconnected and the ignition switch is in the OFF position.

NOTE ON THE SWITCH LIGHTS

When the cluster switch panel is removed, it is a good time to replace burnt bulbs in all the cluster switch panel unit. In my case, one of the bulbs of the wiper switch (the one that is missing in Figure 3) did not work. I could not find an original replacement part, so instead I used Radio Shack 272-1092 micro lamps (12v, 60 ma, 2 per $1.49) and installed it onto the base of the original lamp. Really easy. Mike Gordon suggests to use two of the above bulbs to match the power rating of the original lamp.

INSTALLATION

If the wiper switch and the lights work OK, install everything is reverse order, reconnect the battery and make sure all the switches of the cluster switch panel work properly.