Even if an installer has a wealth of experience in subsequently installing equipment in cars, the best installer will still be prone to making a connection error at some point (thus said the experience expert). Sometimes these are obvious mistakes, after all, we all sometimes have a bad day… but sometimes errors are involved that you could not have pre-empted in advance. This time we will be discussing the consequences of connecting different earth points in a car, for example, when you also have to connect an additional interface/module to ensure the correct performance of the equipment to be installed.
You may have to also install an additional interface/module to ensure the correct operation of different electronic systems. An inbuilt navigation system may, for example, be equipped with a steering wheel module for steering wheel control. It may be the case that the interface cannot be installed directly behind the navigation system for specific reasons and that a different place under the dashboard needs to be used. If there is a good power supply and earth connection at a specific location for this steering wheel module, it is only logical that it will be connected there. However, if we carefully examine this situation, it turns out that there is a real chance of malfunctions occurring should we apply this method. The two systems (the navigation system and steering wheel module) are interlinked by the signals that they send to each other but each of these systems has its own power supply and earthing in this situation. Should one of the earth contacts not make perfect contact with the chassis, for example, due to surplus coating, air or the welding structure of the body, this can already ensure a slight resistance, which may mean that a current will run between the two different earth contacts from one of the earth points through the two systems to the other earth point. Depending on the resistance, this may, without warning, lead to voltage peaks of a few volts on, for example, an output signal of the control module! It is not just the newly connected equipment that can be disrupted due to 2 different earth points. A radio that has already been installed may start to behave strangely if it is in some way a part of the ‘incorrect’ circuit. The recommendation is, therefore, that all equipment that is interlinked should be connected to one and the same earth point and one and the same power supply. To illustrate: the 16-pole Data Link Connector (DLC), that is, the OBDII connector for diagnostics, is itself provided with a chassis earth (position 4) and a signal earth (position 5) to prevent earthing errors in the diagnostics!
