Strange issue

Fabia 1.2, 2013 - Suddenly stops starting. Have been to the workshop several times. They diagnose that the wire plug (couple?) to the ECM (they call it so, is that an ECU?) is loose. Once they tighten, works for few weeks - but the problem comes again. They have advised to replace the plug. BTW, when there is this problem, the left side-light above the front-wheel glows on. What could it be? Thanks!