Schematic Diagrams

Schematics 1988 928s4

Pin and function conventions DIN 72 552

CEB connector numbering

Wiring Diagram

Porsche 928 Electrics WDP Only

Layout of T18 (14p at side wall) connector

Layout of 12pin diagnostic connector

How to read schematics 1990 S4

Location of connections 1990 S4

Location of components 1990 S4


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)

Fuel Octane and Configuration Coding plug


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 repair

Fan motor replacement

Fan running problems

Fan shroud and fan motors

Fan motor fuse panel meltdown

Fan replacement alternative

Intake cool down sensor

Intake temperature sensor

Automatic transmission sensors

Flap and engine cooling design


Battery and Alternator

Battery Choices

Battery Specs and Dimensions (Varta, Berga, Exide)

Battery Ground Strap

More info on battery tech

Battery charging level related to open voltage

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

Battery Charging

Battery Charging FAQ

Ground straps

Ground straps cleaning

Ground points for ECU's  

Ground point VIII in a 928S2

Alternator capacity

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 Bosch bearing repair

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, interlock and idle speed reduction explained

Starter solenoid

Starter schematic simplified

Jump starting a 928

Engine slowly starting

Starter motor assembly and mounting location


Cable loom

Engine cable loom GTS

Engine cable loom GT

Engine loom 1989- S4 GT GTS

Engine loom 89-95 close-up of CEB end

Wiring loom interconnect plug

Wiring loom of 1993 GTS detailed specification

Various pictures wiring loom 1989-1991 S4

Engine bay cable look 1983 928S

Door wiring interconnect T3 T4


Central Electrics Board (CEB)

Blower fuse fried on CEB

Differences CEB

CEB relay layout

CEB detailed pictures

Fuse assembly

CEB maintenance and repair

CEB panels overview part numbers

Windshield drain

Unlocking the connectors on the CEB


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

Central Warning ECU Repair

Center console AC and lock control assembly

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

Bulb controller schematics and wiring

Jumpers / Bridges for the anti theft device

Alarm controller in a S4/GT/GTS

Alarm controller Hella (up to 1990)

Alarm controller Megamos

Alarm anti theft relay in center console

Alarm units overview

Alarm Vent Switch (next to the seat)

Fit Sachs remote control and alarm

HVAC controller and console repair

HVAC controller test

Seat controller

Seat controller electronics

Mirror controller electronics

Central locking controllers

Power window controller inside

Power window controller info and repair

Power window controller difference


Relays and Fuses

Relays detailed info  **

Fuse and Relay changes / year Alan Moore

Fan motor fuse panel meltdown

Fuse and relay chart 1988S4

Fuse and relay chart 1989S4/GT

Relays and Fuses 1992-1995 GTS

Relays and Fuses 1992 GTS



Chime relay, special units

Chime relay, installing the lights-on warning unit

Alarm anti theft relay in center console

AC electrics Clutch Power Relay problems

AC electrics Clutch Power Relay pinning and layout

What is an X - Relay ?

Relay X clacks

Headlight Relay

Headlight Relay versions

Headlight Relay 1982 model (open)

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

Interference suppressor relay

Labels on Relays

How to remove a stubborn Relay

Heat effect on Relays

Troubleshooting #25 fuse in a GTS

Engine keeps running with ignition off (defrost relay)



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


Airbags (see also steering and interior)

Airbag crash sensors

Airbag removal

Fix error air bag system fault 3129/3229

Airbag contact ring

964 (928) Airbag Steering wheel removal

Airbag Components



Door switch fix

Door lock schematic annotated

Keyless entry installation

Keyless entry installation MT400 Waeco


Ignition switch

Ignition switch removal

Ignition switch assembly

Ignition switch problems

Key inserted connector



Wiring Diag help - How to Read the Schematic

How to build a Lambda and MAF meter

GTS won't start, starter lockout

Early car backup lights

9268 tester manual rewritten

Spanner tester Instructions ver 7

ABS tester KDAS0003

Speed sensor wiring in spare wheel area

Engine hood switch

Repairing wire insulation

Center console switch overlay decal


Bulbs and lights

GTS bulbs overview

All the 928 bulbs in overview

Bulb replacement list

Car Bulbs and specs generic overview

LED changeover

LED H4 changeover with cover modification DIY

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

License plate illumination

No reverse light when front lights are off

Brake Light Diagnostic by Rich Andrade



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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