Enter this light bulb replacement project. His brake light needed a new bulb, and he managed to make this 12V LED bulb work in the 6V socket. An LED is a really great choice for this application ...

Almost a month ago I started trying to reverse engineer an inexpensive LED color changing light bulb. With your help ... from the LNK304 datasheet. The 12V output connects to the two VCC points ...

The device uses two 12V-55W light bulbs as the load, using 5A current to take the fully charged battery to 50% capacity which is the safe discharge limit at 12.23V. Arduino is used to log the voltages ...