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A rather simple, basic multimeter is enough to check and troubleshoot the electrical parts of the car. Such multimeters can be purchased at hardware or electronics stores. The picture shows a genuine noname multimeter although I saw the very same unit under many brand names and disguises. Noname meters may not be safe if used to measure higher voltages but in the 12 V network of the car there are hardly other risks than blowing some fuses.

They can measure voltage (Volt), current (Amper) and resistance (ohm). Accuracy is not of utmost importance, however, a somewhat more expensive but robust and reliable multimeter pays for itself in the long run.

Multimeters can be either analog or digital: the analog ones have a traditional needle gauge while digital ones—like the one on the picture--a simple LCD display of generally three or four digits. Digital meters are ubiquitous today and they withstand the rugged environment in a car much better; in addition, you don't have to learn how to read the scales.

A very important parameter of every voltmeter is its internal impedance (measured in ohms per volt). Less important if you measure in the conventional parts of the electrical system but if you want to look around near the electronic circuits (like injection or ABS ECUs), a meter with an impedance of 10 MΩ or more is essential. Analog meters are usually much better in this respect: even cheap ones generally have acceptable impedance, with cheap digital meters you have to be careful (for instance, the one on the picture is rather bad as well).

How to use the meter?

You probably have an instruction manual bundled with the meter but in any way, you'll need a battery inside the meter to supply current for resistance measurement and two probes (wires, usually one red and one black) which plug into the sockets on the meter. About the battery and its location you'll have to consult the manual.

The meter has some sort of a selector switch (a rotary one like on the picture or a series of buttons) to select the required mode of operation. Voltage is represented by V or U, current by A or I, resistance by Ω (uppercase Greek omega) or R. DC (or =) and AC (or ≈) are used as modifiers to denote direct and alternate current. Simpler multimeters have numerous settings, as shown on the picture: each area (DCV, ACV, DCA or Ω) has several settings. For instance, in the 20 DCV mode you can measure between zero and 20 V direct current, in the 20 kΩ mode between zero and 20 kohm or 20,000 ohm). More sophisticated meters have only DCV or Ω modes and they select their actual measuring range automatically, informing you of the unit selected on the display.

You will find at least two sockets on the multimeter, one will be marked COM (common), GND (ground) or will show the circuit diagram of the ground, an arrow consisting of three horizontal lines as shown on the picture. The markings will inform you which is the second socket to be used for measuring V, A or Ω.

What to measure?

You can measure practically everything in your car with this simple meter but at all costs avoid the high tension leads in the ignition system (the ignition coil, the distributor and the spark plugs): they operate at very high voltages which could result in a nasty or even lethal electrical shock. The meter is not capable of measuring such high voltages, anyway.

By measuring resistance you can check whether a wire is broken, a sensor is working or a switch is functional. It is very important to note that while measuring resistance, you have to switch off the current in the circuit (by switching the ignition off or, if this is not enough, by disconnecting the battery). The meter wants to use its own battery to send current into the circuit to be measured and if there is some other current in the circuit, this will falsify the readout completely and can even damage the meter.

Connect the probes to the ground and Ω sockets and select the largest setting of the Ohm mode. If the probes don't touch each other, the meter will show overflow, meaning that the value measured is larger than it can display (the meter on the picture shows a left aligned digit 1, other multimeters will have different ways of displaying this condition—if in doubt, check the manual). In this case, this signals that the resistance between the two probes (as they are not connected) is practically infinitely high. If you touch the two probes together, the circuit will be shorted and the readout drops to zero (or a very small value above zero).

While measuring in practice, you'll look for these two values: overflow or infinity means a broken wire, failing switch or bad grounding contact, while (near) zero an existing and good contact. Connect the two probes to the ends of the cable or connectors of the switch (unless you want to measure an electronic circuit with semiconductors inside, it doesn't make any difference which probe connects to which end) and observe the readout.

To check the functioning of a circuit, measuring voltage is generally more rewarding than measuring resistance. In this case you have to switch the circuit on. Follow the flow of current on the circuit diagram from the battery to the ground and check at each point or connector that you still have the board voltage (12 to 14 V). To accomplish this, connect the probes to the ground and V sockets and select the largest setting of the DC Volt mode (as you can be reasonably safe that there are no hundreds of volts in the car, you can start from the 20 V range or higher). Connect the GND probe to a known good ground (an exposed metal part, bolt or connector) and touch the point to be measured with the other probe while observing the display. If you happen to swap the two probes, the meter will measure all right but will inform you about the reversed polarity by displaying a negative value. As you go along the circuit, you need to find about the same voltage along the path everywhere (a small drop is due to the resistance of the wires and components and is of no consequence but a drop of several volts shows a bad contact). If the readout drops to zero, the fault lies between this point and the last one still with adequate voltage.

The need to measure current is rare, it mostly helps reveal current leaks that flatten the battery. As the battery is capable of supplying rather high currents which could surpass the capacity of the meter, blow fuses or even burn wires and cause fire, it is best left for experienced people who will know how to measure it themselves...

Blower motor

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You might suspect the control module


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Electrical part list

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GSM-DCS mobile phones

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How to connect wires

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When you retrofit items not originally fitted to your car, you often have to tap into wires or make new connections not already present in the electrical circuitry. The best way to do that is by soldering. Although making nice soldered joints requires a little bit of training and experience, it's still far from rocket science. Practice here doesn't mean months or years, much more like five minutes, especially as we're not speaking about soldering delicate semiconductor components on multilayer printed circuit boards but a couple of thick wires...


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Problems with and new installations of front and rear lights.

Missing pixel columns on the LHD display

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The dot matrix display to the left of the steering wheel of the Series II is known to develop an annoying fault: missing pixel columns. Being rather unsightly to look at, this might sometimes completely ruin our enjoyment of the all too common ABS OUT OF USE readout. :-)

Modified windshield wiper

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When it is not raining too hard, the water wiped to the left side of the window, comes back up because of the wind and hinders the view through the windshield. Other cars having only one wiper arm—namely Mercedes—have the resting position on the left side of the windshield. This can be achieved on the BX easily: remove the wiper arm and the plastic cover above the wiper and blower motors. Rotate the small iron arm of the wiper rod mechanism by 180° so that the spindle of the arm would rotate in the opposite position. Replace the cover and re-fit the wiper arm, this time to the left of the windshield.

On the XM

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Before you disconnect the battery on a Hydractive I XM, never forget to wait for the system to release the pressure. If you fail to observe this, serious damage can occur the next time the system is started.

Persistent ABS OUT OF USE display

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We've all seen this readout once or twice in the life of our XM. Rectifying the problem is not always simple although possible. Here we deal with another side of the issue: the display itself.

Retrofitting one-touch electric window

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The GTi and some TZ trim level diesels have a four-function window regulator switch on the driver's door: regular up and down while you push the button, plus an automatic up and down to the appropriate end position with a single push of the button). It is easy to retrofit this unit to another model with simpler electric lifters: go to a salvage yard and find a GTi or TZx with this unit fitted. Remove the door trim panel and separate the secondary panel housing the window regulator switches. You'll need the four-function switch (in contrast to the simpler switch, this has a middle section with the two arrows pointing up and down, plus two outer buttons with a circle marking). The wiring harness starting from this switch goes to a relay unit in the door, then from the unit to the white connector near the bottom of the door (near the radio speaker) plus the other wiring harness connecting the other (passenger's side) switch to the brown connector at the bottom. In your car, you have to swap the regulator switch, the wiring harness and fit the relay unit with three small screws (its place is already there). That's all.

Switches with LEDs

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The XM Series 1 was born in the era of automotive bulbs. When it came to the Series 2, LEDs were already entering the scene. New switches like those on the dashboard started to come with LED illumination but earlier switches retained (and shared with other Citroëns of the time) remained with plain old bulbs: door window, electric seats, some center console switches.

Retrofitting LEDs is a relatively simple process with huge benefits: longevity (practically, eternity) of the LED and the cool operation temperatures are both welcome. Power consumption is lower but it hardly amounts to any tangible amount if only one or two switches are modified. However, with all those pesky switches all around the car, it can even spare two dozen or so Watts.

Trouble with the central locking

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If you have the original remote control fitted, the passenger's side door lock does not activate the central locking by default: the central unit has only two triggering inputs, so Citroën had to use the second one either for that door or for the remote control.


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Troubleshooting the electric circuitry is often feared but is very straightforward in reality.

Start with a copy or printout with the circuit diagram in question. We take an example here, the driver's side electric window of a Series 1 XM.

Which wiper blade to buy?

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I had nothing but bad experience with Bosch wiper blades, be it revolutionary, twin, aerodynamic, whatever. I stick with Champion and Valeo. But one word of caution: when it starts to streak, never rush to buy a new one. Get some alcohol and kitchen paper towel (it's better than Kleenex). Pour some alcohol on the towel, pinch it between your fingernails and literally scrape the blade edge, but hard. Dirt can stick to it with great force. You do this twice or thrice and lo and behold, you blade will probably return to its new condition immediately.

Windscreen washer fluid level

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Yes, it would have been more logical to combine the two reservoirs into one: as we generally use the rear window washer much less often than the front one, its reservoir is usually still nearly full when that of the windshield is already empty. You can improve the situation by connecting the two reservoirs together. Drill a hole into the sidewall of the reservoirs near the bottom. Fit a banana jack into this hole (don't forget to use some sealing gasket or silicone sealant before you secure it with a nut). Fit a plastic tube over the jacks in the two reservoir to form two communicating vessels. If possible, use a tube with rigid walls to avoid it being clamped under liquid bottles or any other item stored in the bulkhead cavity.