DIESEL WAIT LIGHT & GLOW PLUG INFO. ON MULTIPLE SUBJECTS

THIS BULLETIN CONTAINS MULTIPLE SUBJECTS. PAGE THROUGH TO DESIRED SUBJECT.

I. DIESEL WAIT LIGHT STAYING ON - 1981 ALL SERIES. IF A CONDITION IS EN- COUNTERED WHERE THE DIESEL WAIT LIGHT STAYS ON, THE WEATHER-PAK CONNECTOR LOCATED IN THE GLOW PLUG HARNESS SHOULD BE CHECKED FOR PROPER INSTAL- LATION, MAKING SURE THAT A POSITIVE CONNECTION HAS BEEN ATTAINED.

II. DIESEL WAIT LIGHT COMES ON AFTER START UP - 1981 CENTURY AND REGAL. IF THE DIESEL WAIT LIGHT COMES ON AFTER START UP ON CENTURY/REGAL MODELS AND PRELIMINARY DIAGNOSIS SHOWS THAT THIS CONDITION IS NOT DUE TO A MALFUNCTION GLOW PLUG, THE ALTERNATOR DIODE TRIO SHOULD BE CHECKED AS OUTLINED IN THE CHASSIS SERVICE MANUAL. AN INOPERATIVE DIODE TRIO CAN CAUSE THIS CONDITION TO OCCUR, AND NOT NECESSARILY ILLUMINATE THE "CHARGE" LIGHT WARNING INDICATOR.

III. WAIT LIGHT RELAY - 1981 "B", "C" AND "E" SERIES. THERE HAS BEEN CONFUSION RELATIVE TO WHAT APPEARS TO BE TWO (2) RELAYS ON THE COWL OF A 1981 DIESEL-EQUIPPED "B", "C" AND "E" SERIES. ON "B" AND "C" MODELS, LOOKING FROM THE FRONT OF THE CAR TO THE COWL, THE UNIT ON THE RIGHT IS THE "WAIT" LIGHT RELAY. THIS RELAY IS THE SAME AS 1980. THE UNIT ON THE LEFT IS A DIODE MODULE. THE POSITION OF THESE TWO (2) UNITS ARE REVERSED FOR "E" SERIES. SEE 1981 CHASSIS SERVICE MANUAL FOR SERVICE AND DIAGNOSIS.

THE DIODES IN THE DIODE MODULE ARE NOT NEW TO THE DIESEL CIRCUITY. THEY WERE IN THE WIRING HARNESS IN 1980. NOW, TO IMPROVE SERVIC- ABILITY, THEY ARE IN A MODULE. THE MODULE CONTAINS THREE (3) DIODES WHICH ARE PART OF THE CHARGING CIRCUIT AND GLOW PLUG CIRCUIT. THEY PREVENT UNWANTED CIRCUIT FEEDS WHICH, COULD CAUSE THE FOLLOWING:

1. GENERATOR LIGHT WON'T GO OUT.

2. CAR WON'T SHUT OFF WITH KEY.

TO TEST A DIODE MODULE, ALL THAT IS NEEDED IS A SELF-POWERED TEST LIGHT.

1. CONNECT GROUND CLIP TO TERMINAL "C" AND TOUCH THE OTHER PROBE END TO TERMINALS "A" "B" AND "D". THE LIGHT SHOULD LIGHT. IF NOT, REPLACE THE MODULE.

2. REVERSE TEST LEADS AND PERFORM SAME TEST. THE LIGHT SHOULD NOT LIGHT. IF THERE IS A LIGHT, REPLACE THE MODULE.

IV. GLOW PLUG DIAGNOSIS REVISION - 1981 CENTURY AND REGAL. A CORRECTION SHOULD BE MADE IN THE "A" SERIES ELECTRONIC GLOW PLUG CONTROL SYSTEM DIAGNOSIS CHART ON PAGE 6A5-21 OF THE 1981 CHASSIS SERVICE MANUAL. IN CHECKING FOR CONTINUITY IN THE MODULE CIRCUIT BOARD ON THE LOWER RIGHT SIDE OF THE DIAGNOSIS GUIDE THE FINAL STEP IS INCORRECT. THE CHART SHOULD READ AS SHOWN (REFER TO PAPER BULLETIN FOR CHART).

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.