Mirror Housing Turn Signal - Extra Lamp?

I'm in the process of replacing this unit. The replacement unit I purchased is different from that in which is currently installed. The unit has an extra lead & bulb attached to the 2 currently unused pins of the 4 pin wiring plug (see pic).
WHAT IS THIS EXTRA BULB FOR?
I'm just curious if there is some extra feature I am missing!
Thanks guys!
I am a new owner and member, so HELLO! I will be very active around here, so I look forward to conversing with you *******s!!!


Currently installed part #: 41-3135-440
New unit part #: 41-3135-442



