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Intermittent Wiper Relay Replacement
 
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Pelican Technical Article:

Intermittent Wiper Relay Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$10 to $50

Talent:

**

Tools:

Short Philips head screwdriver driver, Mercedes tool 140598023300, 10mm wrench

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Relay

Hot Tip:

Do pull hard on the cluster

Performance Gain:

Working wipers

Complementary Modification:

Check all your gauge bulbs

If your intermittent wipers have stopped working but the regular wiper mode works fine, your intermittent wiper relay has probably failed. Now you are probably thinking great, it's only a relay and while relays themselves are simple to replace, the location of the intermittent relay is a real pain to get at. If you work on cars long enough from time to time you will find things that make you scratch your head and wonder just what were the engineers thinking and the intermittent relay on the w123 is one of those occasions. For some reason the relay is located behind the instrument cluster and to replace it you will first need to remove the cluster. There are a couple of things you need to be aware of; it is a tight fit behind the cluster so do not try and yank the cluster forward when removing it, you will need to reach your hand behind to release a few things to get some working room, also if your cluster is old and you are using the cluster removal tool make sure to make sure it is seated on the cluster and not the front plastic shield as you can pull this straight off the cluster if you do.

Make sure that you disconnect the battery ground cable before you begin as you are going to be working with the cars electronics system.

Over the years your car may have been serviced by multiple people including previous owners and this can lead to parts replaced with different size fasteners and hardware. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches. If something is different on your vehicle please let us know and share your info to help other users. If you have any questions or comments or even a different procedure you would like to share please leave it below and please leave your vehicle information.

We have removed the steering wheel so we could get pictures of the wiring but you do not need to remove your wheel to remove the cluster and change the relay.

Disconnect the negative battery cable (red arrow).
Figure 1

Disconnect the negative battery cable (red arrow). Make sure it cannot make accidental contact with the battery while working.

Remove the five screws holding the under dash panel and remove the panel, please see our article on under dash panel removal for additional information if you need it.
Figure 2

Remove the five screws holding the under dash panel and remove the panel, please see our article on under dash panel removal for additional information if you need it.

With the lower under panel removed you can reach up underneath and push the cluster forward and out from the dash.
Figure 3

With the lower under panel removed you can reach up underneath and push the cluster forward and out from the dash. I prefer to use the cluster pulling tool that Mercedes sells or you can make your won by bending a couple of long pieces of sturdy metal 90 degrees at the end.

Insert the instrument cluster removal tools between the dash and the cluster and turn them 45 degrees so they engage the rear of the housing taking care that they do not damage the material on the dash.
Figure 4

Insert the instrument cluster removal tools between the dash and the cluster and turn them 45 degrees so they engage the rear of the housing taking care that they do not damage the material on the dash. Make sure that the tools are hooking on the side of the housing and not the front glass as this gets brittle over the years with age and if you are not careful you can pull the front shield away from the housing rather than the cluster out from the dash.

Gently pull the cluster forward until you can separate the electrical connections on the left side (red arrow).
Figure 5

Gently pull the cluster forward until you can separate the electrical connections on the left side (red arrow).

Reach your hand in behind the cluster and unscrew the speedometer cable from the rear of the housing.
Figure 6

Reach your hand in behind the cluster and unscrew the speedometer cable from the rear of the housing.

You can now tilt the housing forward and use a 10mm wrench to remove the tach cable (yellow arrow) if your vehicle is equipped with one.
Figure 7

You can now tilt the housing forward and use a 10mm wrench to remove the tach cable (yellow arrow) if your vehicle is equipped with one. In this picture you can also see where the speedometer cable has been separated (red arrow).

Remove all of the other electrical connections and bulb holders and remove the cluster form the dash.
Figure 8

Remove all of the other electrical connections and bulb holders and remove the cluster form the dash.

With the cluster out you still cannot get to the relay, it is located behind the insulation deep back on the left side (red arrow).
Figure 9

With the cluster out you still cannot get to the relay, it is located behind the insulation deep back on the left side (red arrow).

With the insulation moved out of the way you can see the intermittent relay mounted by a single screw to a bracket on the firewall (red arrow).
Figure 10

With the insulation moved out of the way you can see the intermittent relay mounted by a single screw to a bracket on the firewall (red arrow). Use a short Philips head screwdriver and remove the screw and pull the relay out and separate the wiring connection from it.

After all of this, replacing the relay is the same as all the others.
Figure 11

After all of this, replacing the relay is the same as all the others. Installation is the reverse of removal.

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Comments and Suggestions:
Doug Comments: The relay pictured in Figure 11, 107 820 00 10, is the rear window defrost relay, according to the part number. The intermittent wiper relay is just to the right in the picture, part# 000 821 08 63. Am I correct?
July 14, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 

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