Electrical problems are no fun. At least when the engine blows up or the axle dies you can pull it apart,actually see the broken part, and replace the busted piece. You just can't normally see an electrical problem. It often requires meters and test lights to fix, and if you don't know what you are doing, you can do more damage than good.
Over the many years we've been doing this, and the many Jeeps we've been doing it with, we have come across our fair share of electrical demons and figured we'd bring you the top 10 electrical problems, symptoms, and fixes for this special "Most Asked" issue.
Symptom: Gauges function sporadically, Check Gauges light comes on, gauges die while driving
Affected Model(s): TJs and '97-'01 Cherokees (more common on '99-and-earlier models)
Cause: Dirty or loose instrument cluster plug
Fix: Sometimes pulling your cluster out, cleaning the pins, and reinstalling it is good enough. We see the issue pretty frequently on the late '90s Jeeps, and less frequently as time goes on. The connector itself was updated and the updated connector is available from your dealership under PN 05016261 (connector patch harness).
Symptom: Fog lights turn on even with Jeep off; hazard lights don't turn on or don't shut off
Affected Model(s): '01-'06 Wranglers
Cause: Dirty connections in steering column and/or in switches
Fix: Blow compressed air into the headlight switch. If that doesn't work, pull the steering column apart, locate turn signal/hazard switch assembly, and blow compressed air into it and/or take it apart and clean it. If that doesn't work, it's time for a new switch. The stalk-mounted headlight switch seems more susceptible to dirt and moisture than the parts in the earlier TJs and late model XJs. Topless wheeling contributes to these problems.
Symptom: Sporadic instrument/dash light functionality
Affected Model(s): '76-'86 CJ, '84-'01 XJ, '97-'00 TJ, '87-'95 YJ
Cause: Dirty or broken connectors in the dimmer switch
Fix: Pull the switch out and try the compressed air route, or hose the thing off with electrical cleaner while rotating the wheel or knob to clean all contacts. If it's dirty, that should do it. If one of the wires in the potentiometer have broken, no amount of cleaning will do it for you. Sometimes the thin wire that comprises the resistor gets so corroded that only sandpaper or scraping will fix it. Again, be sure to be careful about not breaking that wire.
Symptom: Blinkers and/or hazards flash quicker than a monkey on meth doing semaphore
Affected Model(s): All
Cause: Either you just swapped in LED lights somewhere, or you lost a bulb
Fix: The fast flash is a built-in safety feature to tell you when you've got a bulb out. What is happening is that the impedance in the system has changed to outside the design specifications. If you have a bulb out, replace it. If you've swapped in LEDs and you've got a non-airbag Jeep, the Signal-Stat 262 (two-prong) or 263 (three-prong) flashers will cure your problems. For '97-'00 TJs, the Trico EP-26 flasher now supports LED tail lights. Just grab one at your local parts store, and plug it in place of the old flasher. For a '01-'06 TJ, the solution is now simple with a plug-in replacement five-pin flasher from Gold Coast Distributing (PN GCD-TJ0106).
Woe is Heat
Symptom: Lose speeds on the blower motor switch; lose a range from the mode selector switch, burned smell when heater is on
Affected Model(s): '99-'06 Wranglers
Cause: Often a blower motor short, but sometimes a bad blower motor resistor
Fix: It all depends on how long you let it go. If you catch it early, the fix could be as easy as replacing the blower motor. In our case, the blower motor still had all the ranges, but the heat just stopped working one day ("Jeep Fire Prevention," Oct. '07). We wired in some relays to take the current out of the switch, but ended up with the same problem again due to not replacing everything the first time. You need to make sure the connectors at the switches are in good shape. If they aren't, find a junkyard that has the wires, connectors, and the switch panel and replace them all. Some other things to check are: Pull the blower motor switch apart and check for burned connectors Check amperage of blower motor (should be under 5 amps on high) Check resistor by passengers feet Check voltage at blower motor (look for a bad ground connection)
Symptom: Parking light in dash stays lit after removing brake or doesn't light at all.
Affected Model(s): '76-'86 CJ, '87-'95 YJ, '86-'92 MJ
Cause: If the light is staying on, the tab doesn't pull off the connector correctly. If the light never comes on, it's either a dead bulb or corroded connector/broken wire.
Fix: In the case of the light staying on, the spring in the parking brake assembly is most likely weak. The light will come on with the most miniscule of pedal pressure. Either bend the tab so it is further away, use a bungee cord to hold the pedal up when not in use, or buy a new brake assembly. In the case of the light not coming on, check the bulb in the dash, make sure the connector at the pedal hasn't been kicked off and make sure the contacts on the pedal assembly itself aren't overly corroded. Use some sandpaper to get the bright brass showing again. If none of those do it, look to the wiring, starting at the pedal and working back to the dash.
Cleanliness is Next to Firewall
Symptom: Weird or random functionality of things. Often degrading electrical functioning is noticed.
Affected Model(s): Primarily CJ models, but all mid-1990s and earlier could see these issues
Cause: Over the years, dust, mud, and water can get into the back of the firewall electrical connector and start corroding it. In some instances the factory-supplied grease itself was the culprit.
Fix: Take the block off the firewall and check for corrosion, dirt, or dried mud. Use electrical cleaner and a toothbrush to clean it all up. Some small, fine files can be used to individually clean each connector. Check voltage where it goes into the firewall on the engine side and voltage at the fuse block. If they are significantly different, the problem might be in the block. Use new dielectric grease prior to reassembly.
Wind That Clock
Symptom: Horn stops working, cruise control stops working or works sporadically
Affected Model(s): '95-'01 Cherokee, '97-'06 Wrangler
Cause: The clockspring in these airbag-equipped Jeeps passes the power from the steering wheel down the steering column. The clockspring can be damaged by spinning the wheel while the steering is disconnected, hooking up aftermarket horns incorrectly, and damaged by dirt and/or moisture.
Fix: The clockspring is located behind the steering wheel, and steering wheel removal is necessary to remove it. Unfortunately, it is a non-serviceable unit, so you will have to swap it out. Be careful, though, as it is also responsible for your turn signal cancelling. If your turn signal doesn't self-cancel, you might have busted the ears off the clockspring.
Bad Instrument, Bad Ground
Symptom: Loss of gauges, loss of lights, loss of function of dash-mounted devices (gauges, lights, switches, etc.)
Affected Model(s): All
Cause: The dashboard ground is important to all gauges and switches, not to mention lights in the dash and potentially lights elsewhere in the Jeep
Fix: While the actual grounding point of the dashboard varies model to model, most typically it will be grounded back to the firewall or kick panel near the fuse block. For a quick diagnosis, run a ground wire from a clean metal piece of the dash directly back to the battery. If everything works again, you have found your problem. This only works about half the time, and you may still need to trace wires. Find the bundle of black wires bolted to the body near the fuse block, make sure the connection is tight and clean, then follow the wire back towards the dash, looking for broken wires or bad connections as you go.
Symptom: Low reading on volt gauge, dim lights, sporadic sputtering and possible stalling, and hard starting, to name a few
Affected Model(s): All, but less common on newer models
Cause: If the connections at the battery are loose or corroded, all kinds of issues can occur, including premature death of alternator
Fix: Every time you go under your hood visually inspect the battery connection and give a small tug on the connector and/or wire. Make sure the positive connection is good at the battery, the alternator, and the underhood fuse block or starter solenoid (if equipped). Double check that the ground from the battery goes to the frame, the Jeep body, and the engine block, and that all connections are good. A quick visual will take under a minute once you know where to look. If you are still in doubt after a visual inspection, test the output of the alternator with the Jeep running, and test for power at the battery. They should be very close. If they aren't test down the length of each of the battery cables until you find the issue. Check out Randy's Electrical Corner for more battery terminal options (Aug. '08)