Possibly a stupid question, but here goes 
I have just gone inside my rear light on the 1995 Cali 1100 Carbed version.
It has a normal two way bulb on each side, however, I alsol noticed that there is 3 slots for a spade type bulb too!
I pulled the silver back out and I noticed that there is wiring going to these and so I can put a different type of bulb into it if I wanted to!
What is that for? Is there any reason to have one over the other?
i’d guess this caters for different markets with differing lighting regs. if you’ve got a tail light, a brake light and reg plate illumination, rock on.
Some models have a separate numberplate light bulb as well as two stop/tail light bulbs, the earliest I know of being the Convert. The Cali EV 1993-99 has a separate numberplate bulb too.
Thats about all I can think of too!
Thye go over each other and its a one OR the other thing. Plus, I dont know what bulb goes into that connection either.
Yes, mine are seperate. This is the Stop/Tail light and it just fascinated me that I have not seen this before!
On the Convert the stop/tail light bulbs were 21/5W and the numberplate light bulb 5W
On the EV the stop/tail light bulbs were 21/5W and the numberplate light bulb 10W
Yes, but these bulbs, or rather the connections for these bulbs are physically different. The number plate light is NOT part of this. The tail/stop lights are.
Of course, I was merely intrigued by the fact that it could use one or the other and the other I have not seen before.
For simplicity, I am just going to stick to a standard duel element bayonet bulb like normal.