Pickup ID

[godathunder]

Ive finally got round to cutting a proper bridge for my Shergold project

( https://www.basschat.co.uk/topic/483271-shergold-electric-upright/ )

and excitedly mounted the pickups only to find that silence ensues

 

I assumed that theyre piezos so was expecting a pretty low output but this is zero output. 

Perhaps Im mistaken about them being piezos and they require a polarising voltage.

The jack socket has a 4700pF capacitor wired in parallel across the terminals (Im assuming its for hf rolloff). Ive removed it but theres still no output.

Theyre approx 27mm long and are made of a blue plastic inner with brass/copper folded around. Theyre from the 20th century

Does anyone have any idea what the mystery pickups may be?