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SAE J186-1989: Supplemental High Mounted Stop and Rear Turn Signal Lamps — Design and Compliance Guide
This standard defines design parameters, performance requirements, and installation recommendations for supplemental high mounted stop and rear turn signal lamps on vehicles less than 2032 mm in overall width. These lamps supplement the primary stop and turn signals specified in SAE J586 and SAE J588, improving visibility to following traffic, including through intervening vehicles.
1. Scope and Key Definitions
The standard covers two types of auxiliary lamps: supplemental high mounted stop lamps (brake-actuated steady warning) and supplemental high mounted rear turn signal lamps (flashing direction indicators). The functions may be combined in a single lamp. Vehicles wider than 2032 mm are covered by SAE J1432.
2. Performance and Design Requirements 🛠️
Color: The light from stop lamps must be red; from turn signal lamps, red or yellow, in accordance with SAE J578.
Effective Projected Luminous Area: Minimum 29 cm² measured on a plane at right angles to the lamp axis, defined as the horizontal line through the light source parallel to the vehicle longitudinal axis.
Photometric Requirements: Lamps must meet the zonal luminous intensity values specified in Table 1 of the standard. An orientation adjustment of up to 3° from design position is permitted to achieve compliance. The following Table 2 provides design guideline minima for common test points (for reference; Table 1 is the governing performance requirement).
| Test Point (degrees) | Red Lamp (cd) | Yellow Lamp (cd) |
|---|---|---|
| 10L, 10R | 5 | 8 |
| 10U, V, 10L, 10R (multiple positions) | 10 | 16 |
| 5U,5L, H,V, 5D,5R | 15 | 24 |
| Maximum over any 1/4° cone | 60 | 120 |
Testing: All tests per SAE J575 with modifications: vibration, moisture, dust, corrosion, photometric, and warpage. Warpage test cycles for stop and turn lamps as per J575 Table 1. Plastic optical parts must conform to SAE J576. Color test per SAE J578.
Design Insight: The lamp axis for photometric testing is the horizontal line through the light source parallel to the vehicle longitudinal axis. The lamp under test must be positioned as if mounted on the vehicle.
⚠️ Important: Effective projected luminous area must be at least 29 cm². Supplemental turn signals must flash simultaneously with the required turn signals—not alternately. No other function may be combined except red reflex reflectors.
3. Frequently Asked Questions
What colors are allowed for supplemental stop and turn signal lamps?
Stop lamps must emit red light. Rear turn signal lamps may be either red or yellow, as defined by SAE J578.
What is the minimum effective projected luminous area?
The area measured on a plane perpendicular to the lamp axis must be at least 29 cm².
Can a single lamp provide both stop and turn functions?
Yes, a single supplemental lamp may combine stop and turn functions. No other functions (other than red reflex reflectors) are permitted.
How must supplemental turn signals flash?
Supplemental turn signals must flash simultaneously with the required turn signals, not alternately, to maintain clear communication of intended direction.
