My Belgium LHD 16" LPG'd Syncro Caravelle as an aftermarket (I think) choke type pull knob on the dash which glows green when pulled - very Halloween

I didn't think it did anything, apart from light up when the ignition is on and its pulled, until I was in a very quiet lockup and tried it. I can hear a faint electrical pump type noise coming from the underside of the engine.
Haven't got around to tracing wires yet. The engine doesnt seem to change tone when its pulled, whether on petrol or LPG.
I'll take a photo of the lit knob at lunchtime.
Can anyone shed any light on this?
cheers
Patrick.