Deputy General Manager
Technical Admin. Dept.
Koito Mfg. Ltd.
Dear Mr. Yoshimoto:
This responds to your letter of July 11, 1996, asking for an interpretation of Federal Motor Vehicle Safety Standard No. 108 with respect to the permissibility of a combination turn signal lamp, taillamp, and stop lamp.
In this design, a bulb in Chamber A functions as a turn signal and taillamp. Chamber B functions as a stop and taillamp. A partition partially separates the two Chambers, but ends at a point 10 to 15 mm from the lens.
Standard No. 108 incorporates by reference SAE Standard J586 FEB84 "Stop Lamps" and SAE Standard J588 NOV84 "Turn Signal Lamps for use on Motor Vehicles Less Than 2032 MM in Overall Width". Paragraph 5.4.2 of each of the SAE Standards provides that "[w]hen a stop signal is optically combined with the turn signal, the circuit shall be such that the stop signal cannot be turned on if the signal is flashing." You ask for confirmation that the design of your lamp is such that the stop signal is not optically combined with the turn signal, and that, therefore, the stop signal can remain turned on even if the turn signal is flashing.
We confirm your interpretation. In your design, the stop signal is not optically combined with the turn signal. The bulbs providing the turn signal and the stop signal are in separate chambers, and ought to be perceived as separate signals through the respective lighted areas of their common lens, even though there may be some small incidental spillover between chambers because the chamber partition does not extend all the way to the lens.
If you have any questions, you may refer them to Taylor Vinson of this Office (202-366-5263).
Samuel J. Dubbin