How to fit a 1156 LED bulb into a 7507 housing and vice versa.
You may notice that the 1156 and 7507 bulbs have tabs on the base that do not exactly match. The 1156's tabs are 180 degrees while the 7507 tabs are 150 degrees. These two bulbs may not seem compatible, but there is a very simple modification that can be done to the bulb's base to fit it into the housing.
An example would be a 2007 BMW E90 325i. A product description may advertise the bulb as P21, but that could mean a 1156 or 7507 bulb. Either the 1156 or the 7507 would still be compatible.
Here we have a 1156 LED bulb and a stock 7507 bulb. You can see that the tabs in the 1156 LED are directly across from one another (180 degrees) while the stock 7507 bulb has tabs that are 1/3 from one another (150 degrees).
We are going to alter the 1156 LED bulb slightly to fit into the 7507 housing.
Use pliers or cutters to snip off one of the tabs from the 1156 LED bulb.
You can even sand down the tab, but that will take longer.
Insert the 1156 LED bulb into the 7507 housing and twist to lock.
There shouldn't be any worry that the 1156 LED bulb will slip out of the housing because the single tab will ensure that the LED bulb stays locked into the housing. The bulb is also deep within the housing to stay secure.
This slight alteration works both ways, with a 1156 bulb into a 7507 housing or 7507 bulb into a 1156 housing.