The parallel connection is - as opposed to the serial connection - by far the absolutely dominating method as far as switching in motor vehicles is concerned. Almost all the consumers are switched parallel. Earlier, the fuel injection valves and glow-pins (also called glow-plugs) were switched in series, nowadays both are parallel. Even in trucks, where a 24V circuit exists and where 12V systems have had to be connected, this cannot function with a simple serial connection. This equipment is also - with a special transformer - switched parallel.

Important for the parallel switching is that everything has the same voltage of 12/24 volt. The current divides itself, and thus the, to be calculated, current strength. The quantity of power taken by the parallel switched consumers is added together. That means, (theoretically) that one 5W- and one 21W-lamp, see the above diagrams, can be replaced by one 26W-lamp. Should you be interested in the calculation of a replacement resistance, please click here.