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Porsche928 Electrics(Primary focus - late models: 1987 S4 – 1994 GTS)Alan Moore928-ELECTRICS.COMTHIS FREE VERSION IS THE WIRING DIAGRAM PRIMER SECTION ONLYSEE WWW.928-ELECTRICS.COM FOR NOTES, UPDATES & TO GET THE FULL DOCUMENTTHE TABLE OF CONTENTS FOR THE FULL DOCUMENT IS INCLUDED HERE FOR REFERENCEIf you own the factory workshop manuals & want to workon the electrical system of your vehicle – this is for you!Learn how to read the wiring diagrams, how components& major systems work, basic electrical information, debug& project ideas with examples and much more .1 Copyright Alan C. Moore 2006, 2007, all rights reserved.Registered users may download & print content for their own personal non-commercial use.Republication or redistribution of this content is expressly prohibited without prior writtenapproval of the copyright owner.This guide is for use in conjunction with legal copies of the Porsche 928 Factory WorkshopManuals. No affiliation with Porsche AG or Porsche Cars North America Inc.I can accept no responsibility for the outcome of any actions taken based the information presented in this document.Whilst I believe this information to be correct, you accept full responsibility for its use and any actions you take as aresult, specifically including - but not limited to - work performed on your vehicle.1You may freely redistribute this version of the document that contains only the WiringDiagram Primer content providing these restrictions & copyright remain, the document isunmodifiedis not contributioncombined with/withinany otherdocumentsExcept as explicitlynoted forandindividualsections: Copyrightof therespective owners.Porsche 928 Electrics Copyright 2006 Alan C Moore

PAGE 21FORWARDOK so you’ve purchased the Factory Workshop Manuals (FWM) and are now armedwith everything you could possibly need to know to fix your 928. You open up the wiringdiagrams and select your model year, peer through the 10 triple fold sheets and uh?How do you read these things? What do all these tags & symbols mean? What is “CentralElectric” anyway? what are these numbered circuits?, connecting points?, color codes? etc, Arggh!Well it’s not so bad when you figure out the encoding, which Porsche does not supplysince these manuals were originally intended for Porsche’s dealer service technicianswho also got Porsche supplied training on how to use them.Included here are some explanations of the conventions plus hints, shortcuts & aids tofiguring it all out yourself. Much of this data is applicable to earlier year models althoughsome format and convention changes were made over time. So even if you own a modelolder than 1987 you’ll find the majority of the material still relevant. Systems in thevehicle evolved over time so most are similar to earlier models except as significant newfeatures were introduced.You absolutely need the wiring diagrams for your year vehicle! - these are not provided,and I’m assuming you have access to a complete/legal set, at least for your model year.In addition to the Wiring Diagram Primer that discusses how to understand theconnectivity in the diagrams there are additional sections on electrical constructioncomponents & their operation, basic electric theory you’ll need to know, debugtechniques and some more advanced theory for those interested.There are also some new (previously unpublished) reference documents, comprehensiveexplanations of all the major systems in the vehicle and guidelines on project techniquesfor modifying your 928 electrical systems.I’ve included specific ideas for 20 electrical projects for your 928 with overviews in thedocument and more details in the Project Appendix section. These cover all kinds ofelectrical additions & modifications with appropriate design, fabrication, connection,sourcing and installation considerations.A note on the concept of this document – this is a continual work in progress for me soupdated versions will be released over time - with more information, projects, tips andcorrections. I know I’m fallible and have no doubt got some things wrong and some justgarbled – please let me know of corrections, clarifications or extensions to this material.Please send your comments & updates to me at Document Notes@928-Electrics.ComLet’s dive right in.Porsche 928 Electrics Copyright 2006, 2007 Alan C Moore

THE ‘WIRING DIAGRAM PRIMER’ SECTION (ONLY) ISDISTRIBUTED FREE FOR THE BENEFIT OF ALL 928 OWNERSPAGE 3Porsche 928 ElectricsTable of ContentsALL PAGE NUMBERS ARE HYPERLINKED FOR NAVIGATION[SECTIONS BEYOND SECTION 8 ARE IN THE MAIN 928-ELECTRICS DOCUMENT ONLY]1FORWARD . 2WIRING DIAGRAM PRIMER 9.23.10WIRING OVERVIEW . 14Standardized Wire Jacket Colors . 14Porsche Circuit Numbering. 15Wiring Sizes/Thickness . 15Wire Insulation & Looms . 15WIRING DIAGRAMS STRUCTURE . 16Wiring Diagram & Other Content . 16General Wiring Diagram (WD) Grid. 17Wire Identification .18Wire Connection Conventions . 19Connecting Points (CP#) . 20In Vehicle Location Notation . 20Ground Points (GP x). 21Inter-Sheet Connection Tags . 22Wire Grouping Conventions.23Wiring Looms (WL # or KS #) .23Grouping for Plug & Socket Terminals.24Plug Connectors.244WIRING DIAGRAM (WD) SYMBOLS . 265MODULES . 305.166.16.26.36.3.16.477.17.2Module Identification & Location . 31CENTRAL ELECTRIC (CE) PANEL. 32Central Electric (CE) Overview. 32Central Electric (CE) Physical Implementation . 32Central Electric (CE) General Connectivity. 35CE Connectivity to Other Sheets .35Central Electric (CE) Internal Connectivity . 37TOTAL CONNECTIVITY EXAMPLES . 41Example: Tracing from CE to another WD Sheet . 41Example: Tracing From WD Sheet to CE . 42SCHEMATIC COMPONENTS 4488.1SWITCHES . 44Basic Operation, Symbol & Terminals . 44Porsche 928 Electrics Copyright 2006, 2007 Alan C Moore

PAGE 49INCANDESCENT BULBS . 4810 CENTRAL ELECTRIC (CE) COMPONENTS . 5310.1Relays. 5310.1.110.210.3Special Function Relay Modules .55Fuses . 55CE Plug Connectors. 59BASIC ELECTRIC THEORY 6211 BASICS: VOLTS, AMPS, OHMS & WATTS . 6211.111.211.311.411.5Terminology & Symbols Used In This Section . 62Current (A) . 62Voltage (V). 63Power (W). 63Resistance (Ω) & Ohms Law . 63BASIC DEBUG TECHNIQUES 6512 INTRODUCTION TO DEBUG – THE CHALLENGE . 6512.112.212.312.412.512.612.712.812.9Step 0 – Characterize the Failure. 65Step 1 – Suspect Yourself . 65Step 2 – Check Fuses . 66Step 3 – Basic Relay Checks. 66Step 4 – Check Grounds. 66Step 4 – Check Other Connections . 67Step 5 – Enlist the Support of Others. 67Debug Tools. 68Measuring Amps, Volts & Ohms . 6812.9.112.9.212.9.312.9.412.9.5Use of a Digital (or Analog) Multi-Meter .68Current Measurement .69Voltage Measurement .70Resistance Measurement .71Power Measurements .72MORE ADVANCED THEORY (OPTIONAL) 7313 CHARGE, ENERGY, CAPACITANCE & INDUCTANCE . 7313.113.213.313.4Charge (C) . 73Energy (J). 73Capacitance (F). 73Inductance (H) . 7314 COMPONENT OPERATING DETAILS . 7314.114.214.314.414.514.614.7Resistors . 73Thermistors & Thermal Switches . 74Pressure Switches . 75Inductors (Coils). 75Capacitors. 76Diodes . 76Light Emitting Diode (LED). 77Porsche 928 Electrics Copyright 2006, 2007 Alan C Moore

PAGE 514.814.9Transistors. 78Hall Effect Sensors. 7915 MORE ADVANCED WIRING CONSIDERATIONS . 8015.115.2Wire Insulation Material . 81Wiring Resistance Effects . 8215.2.115.2.2Basic Wiring Resistance Example .82Temperature Effects on Wiring .8316 ADVANCED BULB THEORY . 8416.1Light Output - Luminous Efficiency & Efficacy . 86MAJOR SYSTEM OPERATION 8917 OVERVIEW . 8918 GENERATION, CHARGING & STARTING SYSTEMS . 18.418.4.1Battery . 89BatteryBatteryBatteryBatteryFailure Mechanisms .92Testing .93Maintenance .93Charging .93Alternator . 94Alternator Failure Modes.95Starter. 96Starter Failure Modes.96Parasitic Current Drain . 96Debugging Excess Parasitic Current Drain. .9719 POWER CONTROL & DISTRIBUTION SYSTEM. 9919.1.119.219.2.119.3Ignition Switch Failure Mode: . 102X-Bus (X) & X-Bus Relay. 103Cigar Lighter/Power Outlet. 104Supply-Bus & Supply Relay . 10420 ENGINE CONTROL & RELATED SYSTEMS . 2.220.2.320.2.4Engine Control Systems . 105Theory of Operation LH Jetronic Fuel Injection . 105Theory of Operation EZK Spark Control . 107The Ignition Circuit Monitoring Relay . 108Common No-Start Diagnostics for the Porsche 928. 110Checking the Mass Airflow Sensor (MAF). 114Engine/AC Cooling Fan System. 117Overview . 117Fan Controller Unit . 117Fan Final Drive Stage. 117Air Flap Control System (’87-’90). 11721 EXTERIOR LIGHTING & CONTROLS . 11821.121.221.2.1Main Light Switch. 118Headlights . 119Configuration for Motor Drive & Headlight Switching. 120Porsche 928 Electrics Copyright 2006, 2007 Alan C Moore

PAGE 8.1Headlight Failure Mechanisms: . 121Headlight Remote Aim Adjustment. 122Front Fog Lights & Driving Lights . 123Daytime Running Lights . 123Turn Signals. 124Hazard Switch . 124Marker Lights. 124Front Marker Lights . 125Rear Marker Lights . 127Brake (Stop) Lights . 127Center Brake Light . 128Other External Lighting . 128Reversing Lights . 128License Plate Lights . 128Rear Fog Lights. 128Door Open Safety Lights . 129Parking Light Mode . 129Bulb Monitoring System . 129Failure Modes – Bulb Monitoring . 13022 INTERIOR LIGHTING & CONTROLS . ion & Operation. 130Door Open Safety Lights . 132Interior Light Fixture Removal . 132Failure Modes, Diagnosis & Repair . 133Additional Interior Lighting . 135Additional Interior Lighting Failure Modes . 135Dashboard & Instrument Lighting . 135Dashboard Illumination Failure Modes . 13823 DASHBOARD & DIAGNOSTICS . 13923.123.223.323.423.523.6Analog Dashboard (Pre-1989) . 139Digital Dashboard (1989-1995) . 139Fluid Level, Temperature and Pressure Sensors . 139Brake Pad Monitoring System . 139Additional dashboard features . 139Vehicle Diagnostic Connector . 13924 VEHICLE/DRIVING SAFETY SYSTEMS. 2.524.2.624.3Airbag System . 140Airbag Steering Wheel Removal. 140High Physical Impacts to the Vehicle . 140Windshield Wipers/Washers . 141Front Windshield Wipers . 141Front Windshield Washers with Heated Nozzles. 141Intensive Washer system ( ’92). 142Headlight Washer System. 142Rear Windshield Washers (non-standard) . 142Rear Windshield Wiper . 142ABS System . 143Porsche 928 Electrics Copyright 2006, 2007 Alan C Moore

PAGE 724.424.524.5.124.5.224.6PSD System . 143RDK Tire Pressure Monitoring System . 144RDK Failure Modes: . 145Disabling the RDK system. 146Catalytic Converter Temperature Monitoring . 14725 VEHICLE SECURITY SYSTEMS . 325.3.425.3.525.3.625.3.725.3.825.3.9Electric Central Door Locks . 147Terminology: . 147Central Locking Failure Modes . 149Alarm System . 150Alarm System Overview . 150Alarm System Operation: . 151Test the Alarm Alert! . 151Terminating the armed/alert mode . 152Locking the vehicle without alarm arming . 152Ignition Disable. 153Defeating the Ignition Disable . 153Defeating the Lights & Horn . 154Failure Modes: . 154Intermittent False Alarms . 154Unseen/Unknown Failures . 15526 HVAC & REAR AC SYSTEM . 26.3.526.3.626.3.726.3.8Front HVAC System Operation & Configuration . 156General Operation . 156Configuration: . 156HVAC Head Unit . 157Automatic Temperature Control Setting . 157Re-Circulate (3) Mode . 160Automatic Windshield Defogger Over-ride Mode () . 160Relay On/Off Control & Fan Speed Control . 161Fan Speed Control . 162Night Illumination (incl. AC On/Off Switch). 165Diode Protection (on outputs) . 166Rear (Supplemental) AC System (M570) . 166HVAC Failure Modes:. 167Complete System Failure. 167Blower Fan Failure. 167Blower Fan – Insufficient Airflow/ Excessive Noise. 167AC Not Cold. 167AC Not Cold Enough . 168Noises in Dash . 168Erratic Temperature Control. 169Rear AC Failure Modes . 17127 CONVENIENCE & ENTERTAINMENT SYSTEMS . 17227.127.227.2.127.2.2Cruise Control System. 172Electric Door Mirrors (Controls/Memory). 172All Mirrors (S4 ) . 172Mirror Controls (manual only) . 173Porsche 928 Electrics Copyright 2006, 2007 Alan C Moore