System overview

System overview

Wiring harnesses

Saab 9-5 has eight wiring harnesses: front, power train, dashboard, front door, rear door, roof, tailgate and rear.

They connect all the electrical components in the car to their intended points of connection.

Some components have their own harnesses for distributing power in the component. The electrically adjustable seat is one such example.

Main fuse boxes

Saab 9-5 has two main fuse boxes. One is located on the driver's side between the door and the dashboard, the other is in the engine bay on the left-hand side beneath the windscreen.

The main fuse boxes contain all the fuses and relays except for a relay in the passenger seat which enables the seat to be adjusted without the ignition being switched on.

All the car's maxi-fuses are located in the main fuse box in the engine bay, whereas the ordinary fuses and relays are divided between the two fuse boxes in the dashboard and engine bay.

Power supply

Power supply for the car is divided into:

•	Battery supply

•	+30-supply

•	Power supply (+15 circuit)

•	Power supply (+54 circuit)

•

+X-supply

•

+B-supply

Battery supply

In addition to being supplied to the maxi fuse board 501, the battery voltage is also supplied directly to the starter motor, generator, both lighting relays as well as a number of fuses in the engine compartment electric distribution box and fuse A in the dashboard main fuse box, see .

These leads are unfused and great care must be exercised when measuring the voltage in these circuits.

The charging system is described in service category “Charging Systems” .

+30-supply

When the ignition is in the LOCK position and the key is removed, certain fuses and components are still supplied with power. The power supply comes first via one of the maxi fuses and a certain protection exists against short-circuiting. Also here great care is recommended when measuring voltage before the fuses in the dashboard main fuse box and ignition switch, stalk switch, ignition switch relay, main relay for engine management system and start relay, see .

+15-voltage

When the ignition key is turned to the ON or START position, power is supplied from switch pin 15 to a number of fuses in the dashboard main fuse box, see .

The voltage remains even when the key is turned to the START position.

+54-voltage

In the ON position, voltage is supplied from switch pin 54 to some fuses in the dashboard main fuse box as well as the relay coil at ignition relay 21. The relay draws and voltage is supplied via its switch to fuses both in the engine compartment and dashboard main fuse boxes, see .

When the ignition key is turned to the START position, the current is cut. This is to disconnect a large number of consumers during the start procedure so that the starter motor and engine management system will receive the highest possible voltage and ensure engine start.

+X-voltage

When the ignition key is turned to OFF from LOCK, voltage is fed from the X-pin to the light switch, see .

The power supply is interrupted when the key is turned to the LOCK position.

+B-voltage

When the ignition key has been turned to OFF from LOCK, voltage is fed from pin B to fuse 5 in the dashboard main fuse board, see .

The power supply is only interrupted when the key is removed from the ignition.