I have recently had to deal with several electrical problems. I know very little about electricity in cars so I have had to deal with repair shops about the problems.

1. Driving from CA to AZ the right front turn signal quits and one horn stops working. Took it to a shop in Tucson. Turned out to be corrosion in the right front headlight assembly. It is a used headlight due to a fender bender a couple of years ago. Cleaning all the connections fixed this.

2. Driving from CA to AZ again and the engine light comes on. I discovered that if I put it in delay position for the headlights to turn off I started getting all sorts of fault messages. A check with a code reader said 64 different codes were active!!! Turning the lights off manually and restarting the car brought it back to almost normal, with only the engine light on.
I had the light switch replaced, using the "throwing parts at the problem" approach. The problem seemed to be resolved.

3. A few days later while driving back to CA the whole problem starts up again. First the engine light comes on, then the horn quits, then the left front turn signal quits. Took it to a foreign car service. Wants to replace left front headlight assembly, $1700 at dealer, and a wiring harness, $3000 at dealer, plus labor. That is not going to happen.

Any ideas anyone?

Thanks,
Tom

 

It sounds like your first dealer may have covered this, but just in case... There is a major ground point behind the front right headlamp assembly, visible if you remove the upper radiator cover off. This ground point sounds like the common link to your symptoms. A bunch of wires attach to an Al stud welded to the cross member. Check for corrosion. This stud takes very little torque to shear off, at which point you will need to move the wires to another Al stud. If you have to replace the stud, be sure to use Al.

 

If you have an engine light there will be a code.

Reading the code will give an indication of the source of the fault.

 

Hi Tom,

Just so we don't all chase our tails, could you please tell us the year, model and engine of your Jaguar?

Thanks,

Don

 

Not only did it have a code, it had 64 active codes all at once!!!!

 

04 xj8 4.2

 

So I told the foreign car place to use used parts. Saved some money. After a headlight replacement and part of a wiring harness spliced in the driver's side turn signal works. However the passenger side turn signal quit as I drove out.

Sadly, I am so tired of this that I am ready to get rid of my beautiful Jaguar. We'll see.

Tom

 

I suggest you have the earths (grounds) cleaned also possible bad contacts on clock spring.

 

There are actually three earthing points at the front of the car, two behind the RH headlight, and one behind the LH one. All three can suffer serious corrosion and thus cause high resistance. This then plays havoc with some circuits. Not a very good place to put earths where they get all the salt-laden moisture of countries in the northern part of the Northern Hemisphere !! When I bought my first X350 in 2010, this problem was quite well known, and as my car was on 30k miles I made sure I sprayed plenty of corrosion inhibitor on these earths. I never had a problem with these.

The lighting switch on the steering binnacle is a known fault point too. Not too expensive to replace, and I had to have one on my last X350. I suffered from headlight flickering of increasing frequency culminating on one moonless night on a twisty road when I lost the headlights for about 5 seconds. Doesn't sound like a long time, does it ? However, that "brown trouser moment" experience convinced me to get the problem fixed, and a new switch did the job,.

Best action now is to clear all codes and then if more come up, get them read. It cuts down the investigative workload. I know these things are a nuisance but they are resolvable at not much expense, but you do need somebody who knows about modern Jaguars and modern car electrics, and who has the necessary code reader that reads all the Jaguar codes.

 

Hi Tom,

I apologize in advance for the length of this post - I have to do some work this evening so I won't take the time to edit this for brevity.

Thanks for giving us the year and model of your Jaguar. Without that information, we wouldn't know which electrical schematics to consult. It might also be helpful to know if your car is equipped with HID or standard halogen headlamps.

Many of us have experienced having a long list of codes stored in our X350. Something to be aware of is that a weak or undercharged battery can cause all manner of spurious codes to be flagged, so it would be worth having your battery and charging system checked with a good professional tester (I use a Midtronics EXP-800 that can also test for a bad voltage regulator or rectifier diode(s) in the alternator).

You can download the Electrical Guide for your car here:

Jaguar X350 Electrical Guide 2004

As I studied the electrical schematics with your original post in mind, a question occurred to me: it is possible the turn signal and horn malfunction were not related? Do you use your horn frequently enough to know for certain that one of the horns failed at exactly the same time as the right turn signal failed? The wiring diagrams don't seem to show any explanation for cleaning connections at the right headlamp assembly having any effect on horn function.

The simplest possible explanation for your symptoms is that one of the horns failed independently of the turn signals, and that subsequently the right turn signal failed due to a burned filament in the bulb, or looseness or corrosion on the bulb connector. Soon after, one of those same reasons caused the left turn signal to fail. It is not uncommon for paired bulbs to fail within a short time of each other, and I recall reading that one of our members even had both low-beam headlamp bulbs fail simultaneously.

I tip my hat to rhankey and meirion1 for identifying the ground points behind the headlamps as suspects, and to Fraser for clarifying that there are three of these points. The horns are mounted at the left corner of the front bumper and are grounded at point G1 behind the left headlamp.

Like the body of the car, the ground stud, nut and wire ring/eyelet terminals are made of aluminum. When exposed to moisture in the presence of an electrolyte (salt, many minerals), aluminum oxide (Al2O3) forms on these components in a layer just a few nanometers thin, but since Al2O3 is an electrical insulator, that's all it takes to add excessive resistance to sensitive circuits in the vehicle. This added resistance might be the reason one of your horns stopped working. I posted some photos and information about the grounds behind the headlamps here:

Grounds / Earths Near the Headlamps

Another possible reason for one horn ceasing to work intermittently is that water splashing from the road has filled one of your horns. This is especially likely if your car is missing the plastic valance that is supposed to cover the underside of the front bumper cover. This happened on our '04 XJR. The two horns are hard-wired in parallel to the same electrical connector, so if one of the horns continued to operate, the electrical supply was providing at least some voltage and the ground point was passing at least some current to complete the circuit. I was able to restore the operation of our wet horn by carefully shaking out as much water as I could, then baking it in an oven for an hour at 170 degrees Fahrenheit (the lowest temp our oven would go) with the oven door left open a crack to keep the actual temp a bit lower and to allow steam to easily escape. The horn subsequently failed again, though, so I replaced both horns with a new pair for a late-model Chevrolet that had the correct electrical connector.

The horns are powered via the horn relay (R14) in the Front Power Distribution Fuse Box (FPDFB). The relay is activated by the horn switch in the steering wheel, via the clockspring or "cassette," as it is called on the electrical schematic. The steering wheel horn switch is grounded via the Engine Control Module (ECM) and the ECM's ground point, which on LHD cars is on the right front inner fender, rearward of the suspension tower, near the cabin microfilter housing. As part of the security system, the horn relay can also be activated by the Front Electronic Module (FEM) connecting the circuit to ground.

The front turn signals are not grounded at the points behind the headlamps. They are operated and grounded via the FEM, which is mounted in the left-hand (U.S. driver's) footwell at the base of the A-pillar. The FEM references a ground point nearby on the left-hand A-pillar, and corrosion on this ground point may be an issue. Problems with the FEM have also been suspected but I can't recall whether anyone has actually confirmed the FEM as the cause of exterior lamp malfunctions.

Regarding diagnostic trouble codes (DTCs), I don't see that you've told us the code or codes responsible for the check engine light (CEL), or what was done to resolve the issue.

In addition to the standard P (Powertrain) codes that trigger the CEL, the kinds of issues you've had may have triggered proprietary Jaguar B (Body), C (Chassis) or U (Undefined, mostly network-related) codes that cannot be read by generic OBDII scanners. These can only be read with a dealer-level system or a third-party system capable of reading them. If problems persist, it would be prudent to have the car scanned by a system with this capability.

Cheers,

Don