Moses Ludel’s 4WD Mechanix Magazine – How-to: XJ Cherokee Erratic Gauges Fix

How-to: Jeep XJ Cherokee Erratic Gauges and “No Bus” Fix

The instrument readout is our 1999 XJ Cherokee with the engine running! This not so rare “No Bus” signal and gauge “drop-off” occurs, unexpectedly, on several Jeep models, including XJ Cherokees and TJ Wranglers from the OBD-II era. According to Chrysler’s TSB #08-15-99, the cause on the XJ Cherokee, TJ Wrangler and other models is a defective wire plug. The Chrysler/Jeep recommended cure is Mopar replacement plug and wires kit #05016261AA.

The first time the tach and speedometer dropped to “0” and the Air Bag light came on, we held our breath and waited for the bags to deploy, which they fortunately did not. Would the engine stall? Were we about to watch smoke pour out from the dashboard? Were the instruments fried?

It was a hot summer day at the high desert, the Jeep had parked in the driveway for awhile. The dashboard around the instrument panel was hot, and this would later serve as a clue. When the gauges suddenly jumped back to a normal reading, the cabin had cooled considerably, and the problem did not reoccur until the next time the vehicle heat soaked in the driveway. Catching the “No Bus” signal in the carport that evening launched a search of Chrysler’s service literature for a possible cause.

After a widespread issue cropped up in the late ’90s, Chrysler issued the Jeep TSB 08-15-99. (There was an earlier TSB, this bulletin superseded the earlier release.) Chrysler believed the issue was corroded pins on the instrument cluster wiring plugs.  Click here for a PDF of the official Chrysler bulletin and repair instructions. Read the instruction portion for details and cautions.

The installation of the new plug and wires involves removal of the instrument panel, which is covered in a Jeep factory workshop manual. Here is a summary of the task to help illustrate the repair involved. Accessing the instrument panel is basic. Changing out the plug receptacle and wires does require soldering skills!

Note: Some owners have success simply unplugging the instrument panel and reinstalling it. This might remove corrosion or at least give the contacts a new lease. Claims by some are that this procedure has worked for several years and is still working. Our Cherokee did not manifest a “No Bus” or tachometer, speedometer and gauge drop-off until 130K miles of service. You might try the unplug, clean the contacts as described in the TSB, and reinstall the panel without doing the plug change. If that doesn’t do it, there’s the TSB fix!

Begin with disconnecting the negative battery cable! Accidentally deploying the air bags or frying electrical wires must be avoided. (Cautions about working near the air bags can be found in the Jeep factory service manual.) Note that the negative battery cable is safely away from the post.

Next remove the driver’s side kick panel and shield plate below the steering column for access to the instrument panel bezel.

The center panel comes off by carefully unsnapping the clips. The instrument panel bezel requires screw removal and unclipping. This is a 1999 Jeep XJ Cherokee, likely one of the most practical and simple 4×4 vehicles built since the Jeep CJ era!

The dash panel cover also snaps into place. Unclip the front (furthest from windshield) first. At the angle you see, the panel pulls outward from the windshield end. Clips make this removal and installation simple.

The Mopar #05016261AA new plug with wires is the fix. (Heftier heat shrink tubes are an add-on for wire reinforcement and additional insulation.) Pay close attention to the color code labels. Wire colors are not all matched. The labels indicate where each wire attaches to the factory plug’s wires.

Instrument panel removed, cut the wires near the old plug. Here, heat shrink tubing gets installed before wires are spliced. The first wires get matched, the two ends get an overlap-and-twist splice. Rosin core solder makes a neat bond of the two wires. The heat shrink tubing is kept away from the heat at this point.

Note: In an ideal situation, these wires would be cut on 1/2″ staggers to keep splices apart and reduce the risk of insulation failure causing shorts between wires. However, this spur of the OEM harness has only a few inches of length, which does not lend itself to staggering ten wires! Instead, attention is spent on insulating the wires at the splice with both heat shrink tubing and electrical tape prior to taping the entire section of harness. In the TSB, Chrysler recommends a 1/2″ stagger between each wire splice. Normally, that would be standard procedure for multi-wire splicing.

A classic overlap/twist splice of two wires works well. The aim is to maximize the wire contact to assure adequate amperage flow from one wire to the next. At the same time, the wires have a minimal increase in diameter for bundling within the taped harness. The fully soldered joint has rosin core solder thoroughly saturating the wires—without overheating adjacent sections. Note that heat shrink tube is unaffected.

There are 10 wires on this plug replacement. By splitting the solder chores into two gangs of 5 wires apiece (each row of the plug), the separation makes soldering easier. Always keep adjacent wires away from the soldering tip’s heat. Avoid touching a soldering tip to the insulation of other wires! A tiny screwdriver or pick can be carefully used to stretch a slightly shrunken end of the heat shrink tubing prior to sliding the tubing into place.

Here are five of the wires with heat shrink tubing in place and shaped. Each heat shrink tube was heated with a wooden kitchen match passed carefully along the heat shrink tube—without damaging the tube or any adjacent wiring insulation.

The soldering device is a simple 30W gun, inexpensive and available from sources like Radio Shack. The solder is 60/40 with rosin core. Always use rosin core, never acid core, protect yourself from the lead fumes!

One way to shrink the heat shrink tubing is the wooden match technique. Torches for this task are available but work no better than matches. With practice, you can quickly apply heat to the tubing and shrink it without melting or distorting the tubing or nearby wire insulation.

All of the wires are now spliced. As much time was spent carefully identifying the labeled colors as it took to solder the wires. As added insulation, without the space to stagger the wire splices, each heat shrink tube section gets wrapped individually with electrical tape.

The finished wire splices have 1) heat shrink tubing, 2) electrical tape wrap of each heat shrink tube plus 3) the final harness is double-wrapped with electrical tape to resemble a factory wiring section. Quality electrical tape is UL rated at 600V. The look is OEM, the repair uses OEM Mopar parts, and the final results follow the 08-15-99 Jeep TSB for the “No Bus” and erratic gauges/instruments issue.

Both plugs back in place, this is the alignment for the plugs and instrument panel. Permatex Dielectric Grease* provides added protection against the alleged source for the “No Bus”: corrosion on the plug pins. This vehicle was based at Nevada’s high desert country from day one, so unless there is condensation from defroster or other sources, there is no reason to suspect that corrosion occurred. There was none of the black or gray coating on the pins. We assumed that the plug connector was defective.

Note: There is apparently controversy about the use of dielectric grease. In my experience, this grease applied at plug connectors has helped prevent exactly what Chrysler claims will happen to the pin-to-clip connections at this panel plug, i.e., corrosion over time. A small dab at each of these plug openings will prevent the corrosion claimed to create the problem here. For those still in doubt about dielectric grease, here is a third party YouTube video on dielectric grease. The Permatex official website also has information on the Permatex® Dielectric Tune-Up Grease used on this project. Judge for yourself.

The well insulated new wire and plug harness looks “factory”. Make sure that any extra harness length fits safely beneath the panel cover. This fix looks right and should readily outlast the original plug and wiring! The instrument panel must be aligned carefully with these plugs as you fit the panel into place. Do not bend prongs on the instrument panel sockets!

Four screws retain the panel once the plugs insert fully.  The dash cover and instrument panel bezel fit back in place. The balance of parts reinstall in the reverse order of the disassembly. Make sure everything is in place and fitted properly before reattaching the negative battery cable.