Component Wiring Diagram, Schematic Layout
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All wiring diagrams in this manual are drawn so that the wiring of each separate circuit can be followed up from both the "+" and the "-" side. There are three horizontal lines at the top of each diagram with a "+" feed and at the bottom there is a "-" line to show the earthing.
Each circuit has its current path numerically marked 1, 2, 3 and so on. At current path 1, extreme left, there is the battery "30" wnich is connected to the uppermost of the three horizontal lines (marked in red). This direct contact with the batteries is called "+".
As an example of how to read a wiring diagram and step by step get to know how the circuits function, we have chosen a power supply diagram for a bus with an electrical battery disconnect switch (EBDS). With this we can see that at power path 5 a cable runs with direct positive to the contacts and to the coil in relay 342. In order for relay 342 to be activated, its coil must be earthed via the contacts in relay 361. The coil in relay 361 is voltage-fed from current path 8 across fuse "11" to switch 180 and from there to switch 144. Switch 180 is an emergency switch and switch 144 is the operating switch for relay 342. When this switch cuts in current the coil in relay 361 is voltage-fed and the contacts for relay 361 close the negative side to the coil in relay 342. With this the contact at connections 31a and 31 close and the upper "+" line, which only had contact with the battery, is now in circuit to the centre line called B+ (marked in blue). The battery circuit is now switched on.
To prevent the battery circuit from being mistakingly switched off while the engine is running, there is a "detent" (marked in green) wired to relay 361. When the feed switch 199 (page 6) is switched on, there is voltage to the bottom of the three horizontal lines "T+". The contacts then get voltage also the coil on relay 349 via power paths 10 and 11. At the connection point C8 immediately below the coil on relay 349 there is a reference to a new current path "34". To find the remaining part of the circuit, one must seek under C8 power path 34 (see page 7). Given there is the final reference to the power paths 63, 69, 73 and 75 (applicable to different alternators).