Part 2 of 3

Fig. 1 Backup Lamp Switch - Typical:

BACKUP LAMP SWITCH
Vehicles equipped with a manual transmission have a normally open, spring-loaded plunger type back-up lamp switch. The backup lamp switch is located in a threaded hole on the side of the manual transmission housing. The backup lamp switch has a threaded body and a hex formation near the plunger end of the switch, and an integral connector at the opposite end of the switch. When installed, only the connector and the hex formation are visible on the outside of the transmission housing. Vehicles with an optional electronic automatic transmission have a Transmission Range Sensor (TRS) that is used to perform several functions, including that of the backup lamp switch. The TRS is described in further detail elsewhere in this service information. The backup lamp switch cannot be adjusted or repaired and, if faulty or damaged, the entire switch unit must be replaced.

The backup lamp switch controls the flow of battery voltage to the backup lamp bulbs through an output on the back-up lamp feed circuit. The switch plunger is mechanically actuated by the gearshift mechanism within the transmission, which will depress the switch plunger and close the switch contacts whenever the reverse gear has been selected. The switch receives battery current through a fuse in the Junction Block (JB) on a fused ignition switch output (run) circuit whenever the ignition switch is in the On position. A take out of the engine wire harness connects the backup lamp switch to the vehicle electrical system. The backup lamp switch and circuits can be tested using conventional diagnostic tools and methods.

BRAKE LAMP SWITCH
The plunger type brake lamp switch is mounted on a bracket attached to the base of the steering column, under the instrument panel.

CAUTION: The switch can only be adjusted during initial installation. If the switch is not adjusted properly a new switch must be installed.

The brake lamp switch is monitored by the Instrument Cluster and used for the brake lamp, speed control brake sensor circuits and Electronic Brake Distribution (EBD). The brake lamp circuit is open until the plunger is depressed. The speed control and brake sensor circuits are closed until the plunger is depressed. When the instrument cluster notices the brake lamp switch transition, it transmits a brake applied/released message on the bus. The Front Control Module (FCM) will then illuminate or turn off the brake lamps.

When the brake light switch is activated, the Powertrain Control Module (PCM) receives an input indicating that the brakes are being applied. After receiving this input, the PCM maintains idle speed to a scheduled rpm through control of the Idle Air Control (IAC) motor. The brake switch input is also used to disable vent and vacuum solenoid output signals to the speed control servo.

Vehicles equipped with the speed control option use a dual function brake lamp switch. The PCM monitors the state of the dual function brake lamp switch.

The brake switch is equipped with three sets of contacts, one normally open and the other two normally closed (brakes disengaged). The PCM sends a 12 volt signal to one of the normally closed contacts in the brake switch, which is returned to the PCM as a brake switch state signal. With the contacts closed, the 12 volt signal is pulled to ground causing the signal to go low. The low voltage signal, monitored by the PCM, indicates that the brakes are not applied. When the brakes are applied, the contacts open, causing the PCM's output brake signal to go high, disengaging the speed control, cutting off PCM power to the speed control solenoids.

The second set of normally closed contacts supplies 12 volts from the PCM any time speed control is turned ON. Through the brake switch, current is routed to the speed control servo solenoids. The speed control solenoids (vacuum, vent and dump) are provided this current any time the speed control is ON and the brakes are disengaged.

When the driver applies the brakes, the contacts open and current is interrupted to the solenoids. The normally open contacts are fed battery voltage. When the brakes are applied, battery voltage is supplied to the brake lamps.

The brake lamp switch can only be adjusted once. That is at the initial installation of the switch. If the switch is not adjusted properly or has been removed, a new switch must be installed and adjusted.

Fig.11 ISO Micro Relay:

FOG LAMP RELAY
The front fog lamp relay is located in the Power Distribution Center (PDC) in the engine compartment of the vehicle. The front fog lamp relay is a conventional International Standards Organization (ISO) micro relay. Relays conforming to the ISO specifications have common physical dimensions, current capacities, terminal patterns, and terminal functions. The relay is contained within a small, rectangular, molded plastic housing and is connected to all of the required inputs and outputs by five integral male spade-type terminals that extend from the bottom of the relay base.

The front fog lamp relay cannot be adjusted or repaired and, if faulty or damaged, the unit must be replaced.

The front fog lamp relay is an electromechanical switch that uses a low current input from the Front Control Module (FCM) to control a high current output to the front fog lamps. The movable common feed contact point is held against the fixed normally closed contact point by spring pressure. When the relay coil is energized, an electromagnetic field is produced by the coil windings. This electromagnetic field draws the movable relay contact point away from the fixed normally closed contact point, and holds it against the fixed normally open contact point. When the relay coil is de-energized, spring pressure returns the movable contact point back against the fixed normally closed contact point. A resistor is connected in parallel with the relay coil in the relay, and helps to dissipate voltage spikes and electromagnetic interference that can be generated as the electromagnetic field of the relay coil collapses.

The front fog lamp relay terminals are connected to the vehicle electrical system through a connector receptacle in the Power Distribution Center (PDC). The inputs and outputs of the front fog lamp relay include:
- Common Feed Terminal - The common feed terminal (30) receives battery voltage at all times from a fuse in the PDC through a fused B(+) circuit.

- Coil Ground Terminal - The coil ground terminal (85) is connected to a control output of the Front Control Module (FCM) through a front fog lamp relay control circuit. The FCM controls front fog lamp operation by controlling a ground path through this circuit.

- Coil Battery Terminal - The coil battery terminal (86) receives battery voltage at all times from a fuse in the PDC through a fused B(+) circuit.

- Normally Open Terminal - The normally open terminal (87) is connected to the front fog lamps through a front fog lamp relay output circuit and provides battery voltage to the front fog lamps whenever the relay is energized.

- Normally Closed Terminal - The normally closed terminal (87A) is not connected in this application.

The front fog lamp relay can be diagnosed using conventional diagnostic tools and methods.