A long time ago now, yes. Maybe try an auto parts store? There may even be a "Silicon Chip" kit. Mine came in a bubble pack and was about 20mmX30mmX15mm in size.
Two wires: One on the headlight circuit and one on a wire powered with the ignition. I wired them to fuse terminals so I didn't have to cut the car wiring.
I think that it would be sensible to wire the "alarm" up to a relay that switches the lights off rather than just sounds an alarm. One of my cars has a (factory fitted) chime and I have missed hearing it. Fortunately, there is also a time out system as well
.
I found the card/instructions that came with the unit: Leo Accessories brand, Model LE 100.