If you own an automobile there is a good chance you have an 1157 bulb or similar somewhere on that vehicle. It doesn’t matter if it is a car, truck, van, or even a recreational vehicle this bulb is one of the most popular in use and has been for many decades. Primarily found in tail lights and turn signals it was originally manufactured as an incandescent bulb which was bright enough to be seen from great distances and small enough to be housed in very small containers like under bumper or in fender turn signals. This makes the 1157 bulb the optimal choice for many purposes.
Another widely used function for these small powerhouses is on trailers. Many trailers from small utility type to large over the road containers make use of up to dozens of these bulbs. Because of their brightness many manufacturers rely on them to help improve the safety of their product. Since the original, carbon filament design made use of a dual filament setup it made possible turn signals, brake lights, and running lights all with just one bulb. Previously two bulbs were required for these functions which meant more wiring and more cost of manufacture.
Today the design is available in high intensity LED formats. Because they use the same base and pin configuration the new bulbs can simply be placed in the same location for the same use as their predecessors. Among the advantages of the LED format is brighter light with less energy, longer life, and cooler operation. If you have ever seen an older vehicle with a melted lens you will know those incandescent versions created a high amount of heat. This also caused a possible safety issue which has been eliminated with the newer version.
The 1157 bulb uses two positive connections. If your socket has two connections in the bottom and two slots for pins on the cylinder you probably need this bulb. The two positive connections are so that the same bulb can be used for multiple purposes. The base of the bulb is actually the ground connection and the pins help align the positive connections while assisting in locking the bulb into the socket. Making sure all connection points are cleared from dirt and corrosion is important when replacing or troubleshooting any bulb. Make sure to use a little dialectric grease when replacing lamps to assist in preventing future problems.