Intertwined wire paths are not always traceable

Most current consumers in the Focus have double terminals. But often only one wire can be traced to the battery or alternator. The other ends at some body ground contact, engine, gearbox or other connector tab. For the uninitiated, the currents flow strangely.

Metal parts conduct ground current

Automakers use a physical principle in on-board electrical equipment: metals - electricians call them mass - conduct current. Thanks to this, manufacturers save on wires - quite legitimately - to divert voltage to the negative pole of the battery: in a car, this work is taken over by the body. If the consumer does not work, then the reason is often not in the wire supplying current, but in an incomplete connection to ground. The mass contact then lays strange detours to the target. Consequence: on-board electrical equipment is in complete disarray. For example, you turn on the turn signal, and at the same time the tail light starts flashing to the beat. For an amateur, this seems strange.

Wires and terminals are arranged according to the system

Despite the rational design, the stretched wiring harness in the Focus would stretch for about 10 km. Behind the seemingly chaotic tangle of multi-colored wires lies a system - the colors of the wires show the way. In addition, most of the connections on multi-pin connectors and relays are numbered. When choosing a wire color, the Ford standard uses common examples.

Common wire and terminal designations you need to know

Terminal 15: receives current only when the ignition is on from the ignition switch, while in addition to the ignition, those consumers who should receive electricity only during the operation of the vehicle also receive current. The numerous black wires in the Focus sometimes also have colored extra stripes.


Terminal 30: receives direct current from the plus of the battery or from the generator when the engine is running. If the tools are handled carelessly, this can lead to short circuits or cause a rain of sparks if the wire connected to the battery minus is not removed. These wires, which are always energized, in most cases have a red sheath, sometimes with additional colored stripes.

Terminal 49: refers to the system of intermittent and emergency light signals.

Terminal 53: supplies power to the windshield wipers. Principally green wires marked with other complementary colors (e.g. yellow).

Terminal 56: from it, yellow / black wires supply current to the low beam headlights, and white / black wires to the high beam headlights.

Terminal 58: power is supplied to the front parking lights, as well as to the rear lights and license plate light. The main color of the wire sheath is gray, sometimes with an additional color stripe.

Terminal 31: ground terminal, through which each electrical consumer must be connected to ground. In the on-board network, the corresponding wires have a brown sheath.