By Richard McCuistian

2003 Jeep Wrangler

4.0L Engine

NV 3550 5 speed Transmission

34 ,549 miles

Gauges have always been interesting to me.  The instruments we’re all supposed to watch while we’re motoring around have come a long way since the Boyce radiator-cap mounted Moto meter, but they have always served to give the driver a basic information about how things were going under the hood.  It wasn’t very many years before dash panel instruments found their way into a neat little illuminated cluster that included the speedometer, odometer and the warning lights.  Gauges were bi-metallic for years, driven by variable resistors that responded to pressure, movement of a float, or temperature.

Since first impressions are so important and the instrument cluster is the first thing we notice when we settle into the seat of a vehicle, auto makers have worked tirelessly to keep at least some of their instrument clusters interesting.  GM forged into the realm of a fighter jet style ‘Heads Up Display’ on some of their vehicles, and luxury models in more than one car line began using a peculiar mirror effect on their units in the ‘90’s to produce fluorescent needles that appear to be floating in space instead of being attached to the cluster.  The 2005 Mustang cluster has a decidedly ‘retro’ look.

Some early sixties Oldsmobiles had a mechanical graph-style speedometer indicator that cautioned the driver as the car gained speed by changing colors from green to yellow, and finally  to red at about 80 mph.  Digital electronic instrument clusters with vacuum fluorescent or liquid crystal displays began to appear en masse in the late seventies and early eighties, and these units brought a whole new look to instrument clusters, but most of the motoring public seemed unimpressed, and as a result, while clusters largely remained electronic, the difference was that the newest generation of instrument clusters used their internal hardware and software to interpret signals from other modules (like the PCM or ABS module) on the vehicle network and then display the data with snazzy colorful analog needles rather than digital readouts.

Cluster illumination has been handled a number of different ways, and depending on the vehicle and system.  We can still replace individual instrument panel bulbs on some vehicles, but more and more modern clusters (and dash panel switches) are only serviced as an assembly; some clusters, such as those white-faced units used in Ford Lightning pickups, have no bulbs at all.  International Harvester trucks had an interesting design:  All their switch labels were illuminated with optic fibers fed from a single small bulb mounted in a peculiar flying saucer-looking plastic hub under the dash.

The Jeep Wrangler in question here had what seemed to be a simple concern; no cluster illumination.  In the old days, a simple fuse would have been the most likely cause, but Chrysler’s wiring and their shop manual format transformed an otherwise boring work order into a page-flipping odyssey that can only be appreciated by those of us who have tangled with Chrysler’s sprawling schematics.

I spent several days of my Christmas break working at the Ford/Jeep dealer and this job came to me after having been diagnosed by Jimmie, a graduate of my college auto mechanics department.  He was snowed under with work and the customer was waiting, so the job had to be expedited.

Jimmie had ordered a replacement instrument cluster two months earlier for the illumination concern (the part had been on backorder the whole time), but as I performed my initial inspection I noticed that none of the dash panel switches would illuminate either, and when I tried to grill Jimmie as to why he thought replacing the cluster would fix the other lights that didn’t work, he couldn’t remember.  Jimmie had slept too many times in the intervening weeks to remember why the cluster was his verdict, but he did say the Chrysler hotline engineers indicated that the Wrangler instrument cluster was usually at fault in such cases due to a fairly common short circuit in the console near the shifter. 

Rather than tossing the instrument cluster at the Jeep without knowing the whys and wherefores, I decided to perform my own diagnosis; even if the cluster did fix the problem, it would be conscientious to determine if there was a short anywhere that might cause the problem to reoccur after the cluster was replaced. 

With that in mind, I noticed that somebody had installed an aftermarket radio, and more than once I’ve seen the cluster illumination circuit at the radio connector mistaken for ground and connected to the radio chassis, but a quick look-see indicated that wasn’t the case here. 

This Jeep job was a warranty repair, but the instrument cluster retails for a whopping $600, so imagine what it would be like to replace the cluster as a customer pay job.  That repair bill would ruin just about anybody’s Christmas cheer!  Furthermore, according to the Chrysler shop manual, not a one of the bulbs in that cluster is individually replaceable, and we all know what that means!

 This shifter illumination circuit (orange wire) is a fairly common short point that can destroy the instrument cluster circuitry and put the panel lights out.

Finding the instrument illumination wiring page in the 8W section of the Chrysler shop manual, I discovered that the multifunction switch received its power from fuse F33 in the fuse panel behind the glove box, and that was the most sensible first test point.

The schematic confused me somewhat right from the beginning by indicating that Fuse F33 received its power directly from the battery (the little dialogue box above the MF switch feed said [BATT F33]). 

In reality, F33 fuse is only powered up with the ignition switch in the run position, and I bounced around some thinking I had an intermittent concern with the power feeding that fuse before I realized that the key had to be in the on position for the fuse to show power.  What complicated matters even more at this point was that my test light bulb burned out in the early stages of my diagnostic process, and I had to get past that SNAFU in order to make sense of what was going on.

With power on both sides of the fuse, I attempted to track the circuit from the fuse panel to the multifunction switch, but I had some trouble finding that particular leg of the circuit on Chrysler’s wire map, so I located the Multifunction switch C1 connector pinout map and determined that the MF switch has 4 (count ‘em) FOUR B+ inputs and two grounds feeding it through that connector.  It was a small matter to remove the clam shell trim around the steering column, to uncover the MF switch, but I also had to remove the two Torx® screws that held the MF switch in place in order to shift it for access to the connector.

Since I couldn’t find the wire color or even the circuit number from the pages I had perused in the shop manual (it may have been in the power distribution section, but if it was, I couldn’t find it) and since I wasn’t sure which of the four B+ inputs came from the F33 fuse, I used the shop manual pinout illustration for a guide and checked all four B+ cavities at the C1 connector to find they were all hot.  Now I could forget about everything from the ignition switch through the fuse to the MF switch connector and move on. 

Following the schematic from F33 fuse through the MF switch, I found that circuit L7 (black with a yellow stripe) was shown providing ‘PARK LAMP FEED’ to the instrument cluster. That wire just had to be the one I was looking for… Why else would the instrument cluster need to know if the headlamps were on?  In the absence of any other wire on the schematic doing a similar job, I moved in that direction.

To bypass the MF switch and check the circuit downstream from the MF switch, I used a piece of telephone wire to briefly jump B+ power into circuit L7‘s BK/Y wire and still saw no cluster illumination. The next logical step would be to make sure circuit L7 was continuous all the way to the cluster connector.  Removing the instrument cluster and pulling the pinout map (page 8W-80-30 in the shop manual) for instrument cluster connector C1, I found that circuit L7 made its way into cavity 5 on the C1 connector and in the pinout table for that connector it was labeled ‘HEADLAMP SWITCH OUTPUT.’  This label tends to be rather confusing, since that circuit carries power INTO the cluster and not OUT of it. A tech has to be pretty doggone understanding to get past that and stay on course. On page 8W-51-8 of the Chrysler shop manual, that circuit is pictured and labeled ‘PARK LAMP FEED’ as stated earlier. Why Chrysler’s publisher didn’t use the same label in both places is beyond understanding.  At any rate, with the MF switch reconnected and turned to the park lamp on position, I picked up a nice healthy voltage at the instrument panel connector.

So why didn’t the illumination work?  The lamp ground was present, because the Trip Reset button uses it to trigger the instrument cluster computer and it worked just fine.  The schematic showed an orange wire (Circuit E2) carrying power from the cluster to the external illumination lights on the dash panel switches and A/C controls, and when I fed power into that orange wire, those lights all fired up. 

I had power coming into the cluster, but no cluster illumination and no output to the rest of the dash lights. The instrument cluster was the faulty part, but what had caused it to burn out? Had the Jeep been mine, I would have bypassed the $600 cluster and let the lights burn at full strength all the time!  Removing the console, I located the harness that feeds the PRNDL indicator on AT equipped vehicles, but try as I might, I couldn’t locate a short of any kind anywhere.

The Description and Operation part of each shop manual section is often pretty useful, so I decided to go there and read about this Jeep Wrangler instrument cluster.  What I didn’t expect was that it would be five pages long.  One interesting tidbit I picked up was that the ElectroMechanical Instrument Cluster (EMIC) in the 2003 Wrangler includes all the necessary hardware and software it needs to serve as the Body Controller.

When the driver turns the control ring on the multi-function switch, an analog/digital converter in the EMIC computer receives and converts that input to a digital dimming message, then provides a 12-volt Pulse-Width Modulated (PWM) output to the instrument illumination lamps and the Vacuum Fluorescent Display (VFD) unit on the instrument cluster circuit board, but that isn’t the end of it.  The EMIC also provides a synchronized Pulse Width Modulated output on the fused panel lamp feed output circuit (E2, orange wire) to control the intensity of other illumination lamps such as those on the radio and the illuminated dash panel control switches.

Mid ‘90’s Grand Cherokees had a message center option that provided a rear lamp out warning function, and to make this happen, a fairly simple electronic module is mounted in the left rear corner of the vehicle.  All the current going to the rear lights travels through the Lamp Outage module, and it’s pretty sensitive to current flow through its circuits.  Simply putting the wrong bulbs in the high mount stop lamp can trigger the lamp outage message.  The problem with that entire setup is that the circuitry inside the Lamp Outage Module was weaker than the fuse protecting the circuit.  A short circuit between the module and the lights is supposed to blow the lamp fuse in the panel, but instead, the $40 Lamp Outage Module succumbs to the overload before the fuse does, opens the circuit, and has to be replaced.

The same malady exists on the Wrangler, except that the weak link is a $600 cluster rather than a $40 module.

The Chrysler Hotline told Jimmie that a short circuit anywhere on the orange wire [usually in the console where the orange wire goes to the PRNDL display] can wipe out the instrument cluster, and the reason is that the circuits inside the EMIC are weaker than the 10 amp fuse that feeds the power to the illumination lights.  PRNDL illumination wire goes to the console, even on manual transmission units.

            Installing the new cluster repaired the lights.  I only hope it’s more robust than the original, and if another short circuit happens, maybe replacing the 20 cent fuse will be in order rather than a $600 instrument cluster/body computer!