What is the Approximate Amperage Draw of the ST70RB Sealed Oval Trailer Light

Published 05/02/2011

Question:

looking the amp draw is for the ST70RB light

asked by: Michael

Expert Reply:

The Sealed Oval Trailer Stop, Turn and Tail Light, item # ST70RB, uses an 1157 automotive style bulb with two filaments. The bright filament is rated at 21 watts and the dim filament is rated at 5 to 6 watts.

With the filament wattage, we can determine the amp draw of the bulb. Amperage equals watt rating divided by input voltage. Assuming a 12.8 volts input in all cases, with both filaments lit, the amperage draw would be approximately 2.1 amps. With only the dim filament lit, the amp draw would be approximately .5 amps, and with the bright filament only lit, the amperage draw would be approximately 1.6 amps.

These figures are mathematical and related to the bulb only, the wiring and socket the bulb is attached to will play a role in actual amperage draw figures.

expert reply by: Robert G