Couplers are also consumables. Always check when replacing halogen bulbs.
The coupler is a part of connecting the halogen bulb to the vehicle itself, and the high heat produced by the bulb will be strain on the coupler, so it is always worn out.
When the wear is reached, deformation and other defects may occur, and the worst of couplers and wiring may be burned.
When replacing halogen bulbs, you also check the condition of the coupler and have the following symptoms: Check it out!