Manual - Chapter 6 - Ignition system

6. Ignition HT leads: general

  1. The HT leads are easily removed by withdrawing the HT coil cover (where fitted) and the spark plug cover. Make a note of the routing of each lead before disconnecting and withdrawing it,
  2. On refitting, note that each lead in numbered to identify which cylinder's spark plug it serves. On 75 models the length of the leads will reveal which HT lead is to be connected to which coil, if in doubt note that the HT coil for cylinder number 1 (front) has the black/blue wire, number 2 has the black/red and number 3 (rear) has the black/green wire.
  3. On 100 models the front HT coil serves cylinders 1 and 4, 1 being on the outside (left-hand side) terminal, and the rear HT coil serves cylinders 2 and 3, 2 being on the outside (left-hand side).
  4. In some cases suppressors are fitted to the HT leads; the resistances of these are usually marked on them as on the spark plug caps. If a fault arises, the HT lead can be quickly and easily detached so that its resistance can be measured. If the resistance reading obtained is significantly different from the value specified the component concerned should be renewed.
  5. Always ensure that the leads are correctly routed to prolong as much as possible their service life and if any are to be renewed at any time it is advisable to use only genuine BMW replacement parts so that the correct resistance values are maintained.

Next Section: 7: Spark plugs: general