Electrical Circuit Troubleshooting — general information (Transit 2)

Note: Before starting work, refer to the warnings given in the "Safety First!" section and in section 1. The following tests concern the testing of basic electrical circuits and should not be used to test electronic circuits, especially if they include microprocessor control units.

General Provisions

1. A typical electrical circuit consists of electrical components and various switches, forward or reverse current relays, motors, fuses or links associated with the device, as well as wiring and connectors connecting the device to the battery ("+") and the chassis ("-" or "ground"). To help you troubleshoot an electrical circuit, wiring diagrams for various Ford Transit Diesel systems are provided at the end of this manual.

2. Before troubleshooting an electrical circuit, study the relevant electrical wiring diagram to gain a complete understanding of all components involved in the circuit. The number of possible sources of the fault can be narrowed by noting the circuit components that are functioning properly as you work. If multiple components or circuits fail at the same time, the cause is likely related to a common fuse or common ground.

3. Electrical circuit faults usually have simple causes such as broken or corroded contacts, faulty grounding, blown fuse, melted fuse link, or faulty relay (refer to section 3 for more information on checking the relay). Visually inspect the condition of all fuses, wires, and connections in the suspected circuit before checking its components. Use electrical diagrams to determine which terminals need to be tested in order to pinpoint the exact location of the fault.

4. The main tools needed to find a fault in an electrical circuit are a tester or a voltmeter (for some tests, a 12-volt light bulb with a set of test leads can be used as a voltmeter); ohmmeter (to measure resistance and check the electrical conductivity of a circuit); battery (with a set of instrument ends); shunt wire (preferably with a reverse current relay or fuse included in the circuit), the use of which will help to bypass suspected faulty wires or electrical components. Do not attempt to isolate a fault with test instruments until you have carefully examined the electrical wiring diagram to determine the correct test instrument connection locations.

5. To find a fault in the electrical wiring (usually caused by a worn, dirty connection or damaged insulation), sometimes it is enough to simply move the wires with your hand and see if the problem goes away. This makes it possible to narrow the search area for the source of the fault to a specific section of the installation. The specified verification method can be used in conjunction with any other method described in the following subsections.

6. Besides problems caused by poor connections, there are two main types of faults that can occur in an electrical circuit - open circuits and short circuits.

7. An open circuit is a fault in a circuit such that current cannot flow through the circuit and therefore the component in that section of the circuit will not work.

8. Short circuit type faults are usually caused by a breakdown in the wire insulation, which causes the supply wire to "touch" either another wire or a grounded element such as the car body. A short circuit will usually cause the fuse in the corresponding section of the circuit to blow.

Open circuit detection

9. To check for an open circuit, connect one end of the tester (or the negative lead of the voltmeter) to the negative battery terminal or to a reliably grounded point on the body.

10. Connect the other end to the connector of the circuit being tested, preferably close to the battery or fuse. Voltage should be present at this point if the circuit from the battery or fuse is good (remember that some parts of the circuit are only live when the ignition key is in the appropriate position).

11. Turn on the circuit and connect the end of the tester to the nearest terminal in the circuit on the turned on side.

12. If voltage is present (what can be seen from the tester light or the voltmeter readings), therefore, the section of the circuit between the corresponding connector and the switch is intact.

13. Continue checking the remaining sections of the circuit in the same manner.

14. If a point is found where there is no voltage, then the fault should be looked for between this point and the previous tested point where voltage was present. Most faults are due to a broken, corroded or loose connection.

Short circuit detection

15. To detect a short circuit, first disconnect the load on the section of the circuit being tested (load - these are current-consuming components such as light bulbs, motors, heating elements, appliances, etc.).

16. Remove the appropriate fuse from the circuit section being tested and place the leads of the tester or voltmeter across the fuse connections.

17. Turn on the current (remember that some parts of the circuit are only live when the ignition key is in the appropriate position).

18. If current is present (which can be seen from the control lamp or the voltmeter readings), therefore, there is a short circuit in the circuit.

19. If there is no current during the test, but the fuse still blows under load, this indicates a fault in the load.

"Ground" fault detection

20. The negative terminal of the battery is connected to the ground - the metal parts of the car (engine, gearbox and body). Many systems are connected only to the positive side of the power source. This means that the metal structures of the car are part of the chain. Damaged or corroded components can cause electrical circuit malfunctions. In particular, external (or internal) lights and indicators may glow dimly (especially when the same grounding point is used in another circuit), electric motors (windshield wiper or heater) may work slowly, and one of the circuit loops may influence another that is not directly connected to it. Please note that on many vehicles, the ground strip connects together some components that normally have no metal-to-metal contact due to flexible rubber pads, etc.

21. To check if a component is properly grounded, disconnect the battery and connect one end of an ohmmeter to a well-grounded point and the other end to the point being tested for ground. The ohmmeter should show "zero"; if this is not the case, check the connection as follows.

22. Dismantle the connection and clean the contact points with the body down to bare metal. Carefully clean away all traces of dirt and corrosion, then use a knife to clean the contact area to ensure a metal-to-metal bond. When assembling, tighten the connections securely; if you are installing a wire terminal, use washers between the terminal and the body shell to ensure reliable contact. After disassembling and assembling the connection, protect it from corrosion by coating it with petroleum jelly or organosilicon grease. You can also regularly spray with special lubricating emulsions such as Holts Wet Start.

[The original source of the publication is on the website: FordBook]