Mystery Coil

Just about finished stripping my 1954 D125 and when I opened up the headlamp to make a note of the wiring I found a copper wire coil wound round a spool fitted to a bracket which in turn was fitted to what appears to be a homemade bracket attached to and partly obscuring the top headlamp fixing screw. The coil resistance measures about 2.1 ohm. One end is connected to earth at the lower headlamp fixing screw and the other end is connected by a red wire to the lower right terminal of the paxolin connection board to which the headlight bulb base is fitted to - as seen when the paxolin board and reflector are lowered towards you from the headlamp. (This terminal is directly below one of the copper strips which feed the bulb contacts).
I've searched all the wiring diagrams I can find - both my own and on the internet and none of them show such a coil. Has anyone come across this before or knows what the coil is supposed to do ?
I've searched all the wiring diagrams I can find - both my own and on the internet and none of them show such a coil. Has anyone come across this before or knows what the coil is supposed to do ?