Parking lights turn on when breaking

A few days ago I noticed something odd while driving my car. I noticed that whenever I applied the breaks, my dashboard and radio light came on. After further examination, I determined that all of my parking lights were being turned on whenever I applied the breaks. Furthermore, I noticed that at night, when I intentionally turned on my parking lights, my break lights also remained on. This turns out to be a big  problem, not only legally, but also because other drives do not get a warning that I am applying the breaks during the night. The obvious conclusion is that there must be a short between the break light circuit and the parking light circuit. At this point, I started to think about possible causes which of course could be many. So, I did what most guys would do. I consulted with my dad to see what his thoughts were. He immediately suggested I check the the double filament break light bulb since both the break light circuit and the parking light circuit coexist at this location.  Sure enough, I found the problem here

Break Light Problem

Break light bulb short

The bottom electrical contacts of the light bulb had deformed overtime making a short between them as seen in the pictures above. The diagram below shows what is going  on. Each contact at the bottom of the light bulb correspond to different circuits (parking lights and break lights for example). If a short exist between the two circuits at the light bulb base, applying a voltage to circuit 1 will also activate circuit 2 and vice versa. This is exactly the problem I was having with my parking and break lights.


Simply replacing this light bulb or getting rid of the short between the two bottom electrical pads solved the problem.  So, if you ever have a similar problem, keep in mind that this may not be the only cause. However, this is a very quick check to do during troubleshooting. Also remember to check the female side of the light bulb connection. Here is what my looked like

Break light connection

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