GENERATOR LIGHT FLICKER DURING PULSE WIPER OPERATION

Model and Year: 1988-89 S, T TRUCKS WITH 2.8L OR 4.3L (VIN CODES R, Z) ENGINES

THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 89-219-8A, DATED JULY 1989. THE 1990 MODEL S/T VEHICLES ARE INCLUDED IN THE LATEST BULLETIN ALONG WITH A CORRECTION TO THE ELECTRICAL CONNECTOR NUMBER. ALL COPIES OF 89-219-8A SHOULD BE DISCARDED.

The generator light flicker condition during pulse wiper switch operation in the 1988, 1989 and 1990 S/T instrument panel, with standard cluster, can be caused by negative voltage transients from the wiper motor.

There is no possibility of a system failure as a result of this condition. The effect of this condition is that the generator light will turn on for 80 milliseconds (if gages, the voltage drop on the voltmeter lasts 2.5 seconds). This causes no harm to the generator or other electrical components.

Subject condition can be eliminated by installing a diode (industry part number lN4003) or diode/connector kit (diode kit part number 12085207) in the brown wire at the generator connector (circuit 25 at connector C118). See the following pages in the 1988, 89 and 90 S/T Electrical Wiring Diagrams for circuit 25, connector C118 locations:

1988 4.3L: Section C - Page 24 1988 2.8L: Section C - Page 22 1989 4.3L: Page 40 1989 2.8L: Page 39 1990 2.8L: Page 44 1990 4.3L: Page 45

PARTS INFORMATION:

Quantity Part Number Description -------- ----------- ----------- 1 12085207 Diode

----OR----

1 *1N4003 Diode

*This part available locally.

Parts are currently available from GMSPO.

INSTALLATION PROCEDURE:

1. Disconnect the battery.

2. Remove the connector from the generator.

3. Peel back the black plastic conduit covering the wires.

4. If installing diode 1 N4003: cut out a section of the brown wire that matches the length of the diode.

4A. A diode/connector kit is also available (GMSPO diode kit part number 12085207). If using the kit cut out approximately four inches of the brown wire, following crimping and soldering instructions in the kit. Spiral tape the solder joints and tuck the wire back into the conduit away from the generator. Secure the diode/connector to the outside of the conduit with electrical tape.

5. Solder in diode with the banded end toward the generator.

6. Tape the solder and diode.

7. Reinstall the black plastic conduit.

8. Reconnect connector to the generator.

9. Reconnect battery.

This procedure will not affect the operation of the generator light during the bulb check at the beginning of the start cycle.

For vehicles repaired under warranty use,

Labor Operation Number: T7990

Labor Time: .4 Hr

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.