The magnetic pick-up assembly, on the inside of the distributor, has a permanent magnet, the pole piece having internal teeth and the pick-up coil. This is a small component in the form of a cylindrical drum having radial teeth on its outer shell which engages a toothed wheel on the distributor main shaft within the pole piece. Whenever the teeth of the timer core comes into mesh with those on the pole piece, a varying current is generated from the pick-up coil and by the help of the HEI module is converted into a distributor reference pulse.