SPEED REGISTERS WHEN AT A STOP GLOW PLUGS ON/RE-ROUTE HARNESS

Subject: SPEED REGISTERS WHEN VEHICLE IS STATIONARY AND GLOW PLUGS ARE ON

Model and Year: 1991 C/K TRUCKS WITH 6.2L DIESEL ENGINES

Some owners of 1991 C/K trucks, equipped with a 6.2L diesel engine and an instrument cluster which includes a tachometer, may comment that their speedometer shows a reading during glow plug cycles. The cause of the reading is electromagnetic interference induced into the speedometer circuit by the power circuit which goes to the glow plug controller. The instrument cluster wiring and the glow plug power wire are routed together in the main engine compartment harness that runs from the junction block on the passenger side cowl to various locations in the engine compartment, including the bulk head connector through the left side cowl. The condition may be corrected by rerouting the glow plug controller power wire. Rather than take power from the common junction block on the right cowl, power can be taken from the battery by installing a separate junction block on the left wheel housing.

SERVICE PROCEDURE:

1. Remove the negative battery cables.

2. Locate a relatively flat surface on the left wheel housing just behind the battery (Figure 1). Using the junction block (P/N 459476) as a template, mark two hole locations on the wheel housing.

3. Drill two 1/8 inch (3 mm) holes in the wheel housing and attach the junction block with two hex head screws (P/N 1 1 505023).

4. Remove the air cleaner assembly and cover intake with essential tool J-29664.

5. Remove the cover from the junction block located on the right cowl (Figure 2).

6. Locate the red 8.0 gage power supply wire at the glow plug controller. Trace the wire back to the junction block removing it from the main engine wiring harness as you go. Re-secure the main wiring harness as necessary.

7. Remove the power supply wire/fusible link from the junction block and then reinstall the junction block nut.

8. Install convoluted conduit (Packard P/N 12051375 1/4 inch (6 mm) I/D) on the glow plug controller wire from the controller terminal to the fusible link (Figure 3).

9. Route the wire from the glow plug controller along the left rocker cover and auxiliary battery negative cable and secure it with tie straps (Figure 4).

10. Place the fusible link ring terminal on the previously installed wheel housing junction block. (Figure 1).

11. Using the battery cable (P/N 8907024 or equivalent), cut off the black battery terminal and pigtail and install a red battery terminal from kit part number 1846855 (Figures 5,6, and 7).

12. Using the spacer (P/N 12004189) and the longer battery terminal bolt (P/N 12004188) connect both positive battery terminals to the battery (Figures 8 and 9).

13. Place the ring terminal end of the newly made battery cable and the ring terminal of the glow plug controller power supply fusible link on the junction block stud (it may be necessary to enlarge the terminal hole with a rat tail file) (Figure 9).

14. Place a star washer (P/N 136857 or equivalent) on the junction block stud, then secure both the wires and the washer to the junction block with a hex nut (P/N 11 500424)(Figure 9).

15. Install the junction block cap (P/N 459477), junction block cover (right cowl) and air cleaner assembly (Figure 10).

16. Reconnect the negative battery terminals.

SERVICE PARTS INFORMATION

Part Number Description Qty/Veh ----------- ----------- ------- 12051375 Convoluted Conduit AR 1846855 Auxiliary Battery Terminal Kit 1 459476 Junction Block 1 459477 Junction Block Cap 1 11505023 Screw 2 11500424 Nut 1 12004188 Long Battery Terminal Bolt (5 pcs per box) 1 12004189 Spacer (5 pcs per box) 1 136857 Star Washer (1 00 pcs per box) 1 8907024 Battery Cable 1

Parts are currently available from GMSPO.

WARRANTY INFORMATION

If the vehicle is repaired underwarranty use:

Labor Operation T7476 Labor Time: 0.3 hrs.

Note: Labor Operation is coded to base vehicle coverage in the Warranty System.

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.