Electrical Precautions

GENERAL INFORMATION

03-19

Electrical Precautions

General
The following guidelines are intended to ensure the 
safety of the operator while preventing damage to the 
electrical and electronic components fitted to the 
vehicle. Where necessary, specific precautions are 
detailed in the individual procedures of this manual.

Equipment
Prior to commencing any test procedure on the 
vehicle ensure that the relevant test equipment is 
working correctly and any harness or connectors are 
in good condition. It is particularly important to check 
the condition of the lead and plugs of mains operated 
equipment.

Polarity
Never reverse connect the vehicle battery and 
always ensure the correct polarity when connecting 
test equipment.

High voltage circuits
Whenever disconnecting live ht circuits always use 
insulated pliers and never allow the open end of the 
ht lead to contact other components, particularly  
ECU's. Exercise caution when measuring the voltage 
on the coil terminals while the engine is running, high 
voltage spikes can occur on these terminals.

WARNING: – VEHICLES FITTED WITH BI-XENON 
HEADLAMP BULBS:– The following precautions 
must be observed. Failure to comply may result 
in exposure to ultra violet rays, severe electric 
shock, burns or risk of explosion.

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Safety goggles and gloves must be worn.

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Ensure that headlamps are switched off before 
removing bulbs.

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Do not touch the glass portion of the bulb.

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On no account should headlamps be switched 
on with the bulb removed from the headlamp.

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Bulb testing may only be carried out with the 
bulb fitted in the headlamp.

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Bulbs must be disposed of in accordance with 
local authority bye-laws.

Connectors and harnesses 
The engine compartment of a vehicle is a particularly 
hostile environment for electrical components and 
connectors:

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Always ensure electrically related items are dry 
and oil free before disconnecting and 
connecting test equipment.

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Ensure disconnected multiplugs and sensors 
are protected from being contaminated with oil, 
coolant or other solutions. Contamination could 
impair performance or result in catastrophic 
failure.

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Never force connectors apart using tools to 
prise apart or by pulling on the wiring harness.

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Always ensure locking tabs are disengaged 
before disconnection, and match orientation to 
enable correct reconnection.

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Ensure that any protection (covers, insulation 
etc.) is replaced if disturbed.

Having confirmed a component to be faulty:

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Switch off the ignition and disconnect the 
battery. 

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Remove the component and support the 
disconnected harness.

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When replacing the component keep oily hands 
away from electrical connection areas and push 
connectors home until any locking tabs fully 
engage.

Battery disconnection
It is imperative that the key is removed from the 
ignition before disconnecting the battery. A time of 2 
minutes must also elapse before disconnection. 
Failure to do so could result in: 

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Navigation computer hardware damage

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Incorrect fuel gauge reading

Before disconnecting the battery, disable the alarm 
system and switch off all electrical equipment. If the 
radio is to be serviced, ensure the security code has 
been deactivated. 

CAUTION: Never disconnect the battery with the 
ignition switched on.

CAUTION: To prevent damage to the navigation 
computer hardware, a waiting period of two 
minutes must elapse after the ignition is 
switched off before the battery leads are 
disconnected.

CAUTION: To prevent damage to electrical 
components, always disconnect the battery 
when working on the vehicle's electrical system. 
The ground lead must be disconnected first and 
reconnected last.

CAUTION: Always ensure that battery leads are 
routed correctly and are not close to any 
potential chafing points.