For most of the time since I bought the car it’s been flashing, but now it’s constantly on. And it’s happened once or twice before but went back to flashing after about 15-20 minutes of driving. Maybe just old wiring. Attaching some pictures for clarity. Light diode wire carrying tag YWN10002...

Bit late to the party, but having this exact same problem, in a 1998 110 CSW 300tdi I bought last year. Everything alarm or immobiliser related seems disconnected but still in place, also has series doors, and no key fob. But has this tiny red light that’s been flashing in an alarm fashion...