Interpretation ID: nht68-2.7

DATE: 06/19/68

FROM: AUTHOR UNAVAILABLE; David A. Fay; NHTSA

TO: Robert Bosch Corporation

TITLE: FMVSS INTERPRETATION

TEXT: Thank you for your letter of May 24, 1968, to Mr. J. E. Leysath of this Bureau, concerning the testing of automotive flasher devices.

Motor Vehicle Safety Standard No. 108 specifies that turn signal flashers and vehicular hazard warning signal flashers conform to SAE Standards J590b and J945, respectively. These SAE standards, in turn, require that the test circuitry and test instrumentation conform to SAE Standard J823a. As you noted, the distribution of the 0.10+/-0.01 ohm series resistance in the standard test circuit (Figure 1 of J823a) is not specified in SAE Standard J823a. Therefore, your recommended distribution, namely, 0.025+/-0.005 ohms resistance between the power supply (positive terminal) and flasher input terminal, and 0.075+/-0.005 ohms resistance between the flasher output terminal and the flasher bulbs, would be permitted by SAE Standard J823a.

Flasher units having a ground terminal that is connected with the negative terminal of the power supply may be tested in the standard test circuit of SAE Standard J823a, provided the ground circuitry does not change the required resistance of 0.10+/-0.01 ohm looking into terminals A-B with the removable shunts in place (see note for Figure 1, SAE J823a).

The above-stated test provisions in no way except the flasher units from meeting all performance requirements specified in Standard No. 108, including those specified in basically referenced SAE Standards J590b, "Automotive Turn Signal Flashers," and J945, "Vehicular Hazard Warning Signal Flasher."