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SAE J589b-1977: Turn Signal Switch Standard โ Key Requirements and Testing
🛠️ This standard specifies durability and performance requirements for automotive turn signal switches, ensuring reliability under extreme conditions.
Switch Classes and Environmental Testing
SAE J589b defines two classes of turn signal switches based on vehicle width. Class A switches are intended for vehicles 80 inches or more in overall width (e.g., trucks and buses), while Class B switches are for vehicles less than 80 inches wide (e.g., passenger cars and motorcycles). A Class A switch may be used on any vehicle, but the classification ensures appropriate robustness for larger vehicles.
Temperature testing verifies basic functionality. The switch must be manually cycled 10 times at design load after one hour exposure at 75±10°F, 165+0−5°F, and −25+5−0°F. It must remain electrically and mechanically operable at each extreme.
Endurance Testing Setup and Requirements
Endurance testing simulates long-term usage. The switch is operated with maximum design bulb load (excluding the flasher). Failed bulbs must be replaced during the test. If the switch has a self-canceling mechanism, the test equipment must allow both self-canceling and manual canceling.
One cycle consists of the sequence: off, left turn, off, right turn, off. Timing requirements: travel time 0.1–0.5 s maximum per position change, dwell time 0.4 s minimum per position, at a cycle rate of 12–20 cycles per minute.
Power supply must meet strict specifications: voltage at switch input (6.4V/12.8V/25.6V depending on system), dynamic regulation within 1.0V deviation, recovery within 5 ms, static regulation within 2%, and ripple voltage max 300 mV peak-to-peak.
| Requirement | Class A | Class B |
|---|---|---|
| Total cycles | 165,000 | 100,000 |
| Self-canceling portion | 155,000 | 95,000 |
| Manual canceling portion | 10,000 | 5,000 |
| Stop lamp circuit fed (initial cycles) | First 100,000 | First 50,000 |
| Cornering light circuit fed (if from headlight switch) | First 50,000 cycles | |
⚠️ Important: Failed bulbs must be replaced throughout the endurance test. Stop lamp circuitry needs to be electrically fed only for the specified initial cycles.
Voltage Drop and Combination Switch Requirements
Voltage drop from input terminal to lamp terminal is measured at the start and every 25,000 cycles. Limits depend on the number of lamps per side:
| Lamp Load per Side | Maximum Voltage Drop |
|---|---|
| 2 or less | 0.25 V |
| 3 | 0.30 V |
| 4 | 0.35 V |
| 5 or more | 0.40 V |
If wiring is integral to the switch, the measurement includes 3 inches of wire on each side. Care must be taken to exclude voltage drops from other devices.
Engineering Design Insight Monitoring voltage drop throughout endurance testing is critical. Exceeding the limits indicates increased contact resistance or wiring degradation, which can lead to dim or intermittent turn signals. Designing for low and stable contact resistance is essential for long-term reliability.
For combination turn signal and hazard warning switches, both functions must be tested on the same switch. The hazard warning function must comply with SAE J910b and must have a distinctly different actuating motion from the turn signal function to prevent accidental activation.
Frequently Asked Questions
What temperature ranges must the switch withstand?
The switch must operate after one-hour exposure at -25°F (-32°C), 75°F (24°C), and 165°F (74°C).
How many endurance cycles are required for Class A vs. Class B switches?
Class A requires 165,000 cycles (155,000 self-canceling + 10,000 manual if applicable). Class B requires 100,000 cycles (95,000 self-canceling + 5,000 manual).
How is voltage drop measured and what are the limits?
Voltage drop is measured from input terminal to lamp terminal, including 3 inches of wire if integral. Limits range from 0.25V for up to 2 lamps per side to 0.40V for 5 or more lamps per side.
What distinguishes Class A from Class B turn signal switches?
Class A switches are intended for vehicles 80 inches or wider (trucks, buses), while Class B switches are for narrower vehicles (cars, motorcycles). Class A has higher endurance requirements.
