How to Replace a Rear Bicycle Light

As opposed to a bike headlight, which is usually cylindrical in shape, a rear bicycle light is most often squarish or half-sphere shaped and smaller than its front counterparts. Because they are more compact than front lights, they often are too small to hold standard AA or AAA alkaline or rechargeable batteries, but not always. Some use micro disc batteries that are 1.5 volts each. Others use rechargeable Li-ion batteries. Since there are so many types of rear bicycle lights on the market, each with their own specific design, removing and replacing the light requires different steps for different lights. The example used here is for a Trek rear bicycle light.

Step 1: Remove Back Plate

In order to replace one of the LEDs in a rear bicycle light, first remove the back plate. Rear bike lights don’t usually have a twist-off cap. Rather, there is a small tab into which a quarter fits perfectly. Slip the edge of the quarter into the tab and attempt to twist the quarter. The two sections of the plastic case should come right apart.

Step 2: Remove the Batteries

This particular rear bicycle lights uses 2 AAA batteries. Other lights may be different. Pull the batteries out from between the terminals and set them aside.

Step 3: Unsolder the Bulbs

Heat up the soldering iron and, when ready, melt the solder away from the points at which the bulb or bulbs attach to the circuit board. The two prongs of each light bulb will stick through the board and be surrounded by a small mound of solder. To get to one bulb to replace it, you may have to unsolder all of the bulbs. The Trek rear light uses 3 LEDs. There will also be a metal clip connecting each battery to the circuit board. In order to remove the board to get to the bulb, this clip will also have to be unsoldered. However, you may be able to use the pliers to pull out the terminals with the circuit board.

Step 4: Replace Bulb

Pull the dead bulb out from where it rests and replace it with a like bulb. Reinsert the circuit board, making sure the 2 points of each bulb go back through the circuit board in the same manner.

Step 5: Solder the Connection Points

With the solder and soldering iron, reconnect the points to the circuit board. Make sure the soldering connection is clean or else the light may not work. Also make sure that the terminals are back in their original position and that the metal connectors are in no way damaged. 

Replace the batteries and put the back plate back onto the rear light. Check the switch. If all was done correctly, all of the LEDs should work like new. If, for some reason, the light does not work, open it back up and check your soldering connections. The batteries may need to be changed out or recharged.