Curbside Tech: A Deep Dive into GM Wiper Systems, Part 1


Wipers cleaning windscreen — Image by © Volker Moehrke/Corbis

Living in the arid west, I feel every car should come with intermittent wipers as a standard feature. Unlike the Mid-west, where rain comes in two forms (wet and even more wet), the states anchoring the southwestern corner of country almost never see normal rain. Instead, we see “just a little drizzle,” or “so much damn water you really ought to park the car.”

This is the stalk I need to see!

Because of this, I planned to add intermittent wipers to the El Kylemino, but was not very familiar with GM wiper systems. To address this gap, I started a research project to see what it took to convert standard GM wipers to intermittent. The web gave me lots of information up front, but half of it conflicted with the other half. In addition, I encountered odd phrases such as “depressed park,” “pulse board,” and “pulse relay.” Clearly, I needed to build my understanding of GM wiper systems before I could convert my car to the desired system.

Today, I’ll share this research with you, and explain how GM wiper systems evolved into the system used on the 5th generation El Camino. Next time, we’ll start all over because of a major change GM made to the wipers in 1984 (those bastards!).

Depressed park wipers- The linkage in the red circle moves the wipers from “I” to “P” (the blue wedge)

The story behind this week’s wiper system goes back to 1968, when the engineers at GM developed a hidden wiper system for many of their models. By building a well in to the cowl of the vehicle, and then cantilevering the back of the hood over this space, they created a “cave” to hide the wiper arms when not in use.  To park the wipers in this space, the engineers built a new wiper motor and transmission designed to retract the wiper arms below the base of the windshield.

The abstract from GM’s patent application- Clear as mud

If that sounds a bit complicated, you’re right. In order to make everything work, the designers created a unique control circuit using a “park relay.” During operation, the wipers move up from the park position prior to sweeping the glass, and then retract after of the final sweep. Adding to the complexity, the engineers also used a “switch to ground” circuit, which means the control switch is on the ground side of the circuit, instead of the power side.

To add to the confusion, on certain lower priced name plates (think Chevy), GM chose to offer the hidden wiper feature as an extra cost option. That meant the factory had to keep track of different switches and motors used during assembly, since the parts are not interchangeable between the two systems. In fact, the second generation Camaro parts book shows 10 different wiper switches. However, by 1975 GM made hidden wipers standard on most of their cars supporting the feature, including the El Camino.

Washer Pump in the Motor Cover- The piston and cam are highlighted in the red circle

As a final piece of the puzzle, on many GM wiper motors, the gear box also ran piston style washer pump driven by the wiper motor. To use the pump, a solenoid in the motor cover engages a four lobe cam that drives the pump piston. Of course, the El Camino also used this feature.

During intermittent operation, the blades pause in position “I”

In 1974, GM added an option called the “pulse wiper,” a feature most people call intermittent wipers. Rather than redesigning the system, they adapted the existing parts to work as intermittent wipers. During operation, the wiper blade paused at the end of each sweep, and remained on the glass until the next intermittent sweep. The arms only moved to the depressed park position when the driver turned off the wipers.

If a wiper motor assembly includes the terminal circled in the left image, there’s a circuit board for the intermittent wipers under the black cover

To keep things simple, GM designed the pulse wiper system to piggy back on the existing motor. The cover containing the wiper motor became a “pulse cover” and now included a circuit board with an additional terminal for a new signal wire. GM also cut the motor power wire in two and added a pair of terminals so the wire could connect to a “pulse relay” inside the pulse cover.

Column switch on the left- MUCH harder to replace than the traditional dash switch

The fifth generation El Camino used this system when it was released in 1979, but GM wasn’t done making changes. In 1982, they moved the wiper switch from the face of the dash to the base of the turn signal switch in the steering column. With this change, you now had to pull the steering wheel and remove the turn signal assembly to get to the wiper switch.

So as you can see, there are many variations to GM wipers over these years. Technicians working on GM wipers needed to determine if the car was equipped with standard wipers, depressed park wipers, or depressed park wipers with pulse (intermittent) wipers. In addition, they needed to determine if the wiper motor cover included a washer pump (not every depressed park system did). But at this point, I was confident I had identified every possible GM depressed wiper system variation.

Based on this information, I built the list of parts required to install intermittent wipers in the El Kylemino:

  • A new wiper switch in the steering column.
  • An additional wire from the switch to the motor (unless GM included the wire in every harness).
  • A motor pulse board (including a washer pump).
  • A new wiper motor (if I could not modify the existing power wire to work with the pulse board).

’87 El Camino wiper motor- Something does NOT look right here…

However, before I started the project, I discovered the source of that conflicting information I mentioned at the top of the post- In 1984 GM tossed EVERYTHING out and developed a completely new system with an entirely different motor, pulse board, and circuit design. Time for some more research…

More on GM wipers:

Part 2

Part 3 (coming soon)