348tb third brake light bulb

I accessed the back of the third brake light
located in the centre rear of the engine bay lid in my
1993 model 348tb as the light wasn't coming on
with the other two rear brake lights.
I found a small black electrical connection with
one red and one black lead but no sign of a bulb.
The prongs on each side of the connection are only
around 2mm wide and I can't for the life of me
find a bulb that suits. Can anyone advise me where
to buy this bulb and describe what it looks like.
It must be very small.

 

I can't believe no-one has ever accessed and changed one of these brake light bulbs in their 348 third brake light. All-glass bulbs are available but they have a horizontal base so they wont fit the connector as it has distinct positive and negative ports with a plastic gap in the middle.

 

Here is a pic of the connector unit Alden ....
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