Schematic Diagrams

Schematics 1988 928s4

Pin and function conventions DIN 72 552

CEB connector numbering

Wiring Diagram

Wiring Loom 1989- S4 GT GTS

Porsche 928 Electrics WDP Only

Layout of T18 connector

Layout of 12pin diagnostic connector


Electrical Engine related

Fault codes

The Diagnostic tool and fault codes

Fault code 1214

Start problems and power connections

Powering Fuel pump, LH and EZK

Ignition/Switch/Starter problems

Ignition switch assembly

Engine not turning over

Sometimes it won't start: starter relay

S4 control unit coding (GAS octane)


Cooling Fan

Fan Power stage repair

Fan Power stage repair service

Fan Power stage repaired

Fan controller module repair

Fan control unit troubleshooting

Cooling Fan system Sensors

Cooling Fan funny business

Cooling fan circuit explained

Testing the Fan power and fan operation

Fan motor reconditioning

Fan motor internals and repair

Fan motor replacement

Fan running problems

Fan shroud and fan motors

Fan motor fuse panel meltdown

Intake cool down sensor



Battery and Alternator

Battery Choices

Battery Specs and Dimensions (Varta, Berga)

Battery Ground Strap

More info on battery tech

Car Battery FAQ

Battery terminal connections

Battery drain

Battery drain issues

Batteries testing current draw checking proc

Battery drain probing and short circuit tester

Battery maintenance and charging

Battery maintenance

Ground straps

Ground straps cleaning

Ground points for ECU's  

Alternator Pictures and info 115A version

Alternator wiring

Alternator cooling

Alternator and Resistor types in pre-S4

Alternator woes: (lack of) charging

Alternator charging failure  

Alternators and charging

Alternator or battery dead

Alternator Rebuild 115A

Alternator Rebuild

Alternator Regulator repair

Alternator (Lichtmaschine) Überholung

Alternator test

Alternator testing

Alternator models and specs

Alternator Brushes and parts

Alternator Diodes testing

Alternator belt almost broken

Alternator Parts Bosch

Voltage adjustable Regulator

Voltage fluctuations

Voltage low

Voltage problems and over-voltage damage



Starter motor assembly and mounting

Starter does not work

Starter solenoid

Jump starting a 928

Engine slowly starting

Starter motor assembly and mounting location


Cable loom

Engine bay cable loom GTS

Layout of T18 connector

Wiring loom interconnect plug


Central Electrics Board (CEB)

Blower fuse fried on CEB

Differences CEB

CEB complete layout

Fuse assembly


Electrical Maintenance Job

Annual Electrical Maintenance

*AMP connectors and repair




Control Units

Control Units Annotated view and parts **

Control Units locating

Cruise Control unit repair

Cruise Control connector pinning

Cruise Control understanding the VDO Amp

Cruise Control unit actuator

Resetting the Brake Warning light

Diagnosing central warning light

Repairing Central Warning Unit

Central Warning Light explained

Central Warning System Repair

Diagnosing the Tail Light warning light

Bulb controller problems

Bulb check controller and LED bulbs

Bulb (lamp) check unit bypass

Bulb (lamp) control unit modification

Bulb control unit differences

Jumpers / Bridges for the anti theft device

Alarm controller in a S4/GT/GTS

Alarm Unit Hella (factory) disable

Alarm controller Megamos

Keyless entry installation

Keyless entry installation MT400 Waeco

Fit Sachs remote control and alarm

HVAC controller and console repair

Seat controller

Central locking controllers

Power window controller inside

Power window controller info and repair


Relays and Fuses

Relays detailed info  **

Fuse and Relay changes / year Alan Moore

Relays and Fuses 1988 928S4

Relays and Fuses 1992 GTS

Chine relay, special units

Chine relay, installing the lights-on warning unit

AC electrics Clutch Power Relay problems

AC electrics Clutch Power Relay pinning and layout

What is an X - Relay ?

Relay X clacks

Headlight relay

Water leaking on the relay panel

Fuel Pump relay bypass

The FCU relay (XIX)

ABS Pump Relays

PSD pump Relay

Seat heating relay

Daylight Running Lights relay

Labels on relays

How to remove a stubborn relay

Heat effect on Relays

Fan motor fuse panel meltdown



Where to take 12V accessories power from


Bosch docs

Bosch sensor information

Bosch knock tech

Bosch Fuel Injection Systems


Bosch Technical Instruction-Jetronic

Bosch Technical Instruction L-Jetronic



Airbag crash sensors


Ignition switch

Ignition switch removal

Ignition switch assembly

Ignition switch problems




Warm-up valve operation

Wiring Diag help - How to Read the Schematic

Door switch fix

How to build a Lambda and MAF meter

Early car backup lights

9268 tester manual rewritten

Tester Instructions ver 7

GTS won't start, starter lockout


Bulbs and lights

GTS bulbs overview

All the 928 bulbs in overview

Bulb replacement list

Car Bulbs and specs generic overview

LED changeover

Third brake light

Fog lights LED conversion (for daylight driving lights)

Converting Interior Lighting to LEDs by Ed Scherer

Interior lights

Interior lights stay on

Hood light pre 1990



Note: all of the technical information is provided without any filtering. Any damage caused by using or applying the information is the risk of the reader. The publisher (me) can not take any legal responsibility whatsoever. Please do not use any information from this website if you do not accept this condition.

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