Hello all,
I am trying to change a Passenger side low beam headlight for my Jaguar XJ8L 2005. The connection was broken (crumbled last time when I changed the bulb) and loose. The light was not working so I have ordered a new H7 wire harness.

While I am waiting for new wiring harness, I tried to put hot glue on the connection so that it will not move. It initially worked but afterwards I found the light stopped working again. I checked the voltage between the two connectors and it shows 0 instead of 12 V. I connected other working bulb to this and no light.

Can you please suggest if there are any remedies that I can perform to check fuse (other 3 lights are working) or wiring issues?

Thanks in advance.

Kind regards,

 

Hi Anant,

Just to clarify, are the low beams on your car H7 halogen/xenon bulbs, or are they D1S HID burners? Both systems receive power via relays in the Front Power Distribution Fuse Box, but the HID system also incorporates ballast circuits mounted on the bottom of each headlamp assembly.

You can download the 2005 XJ Electrical Guide at this link, courtesy of our forum member Gus:

http://www.jagrepair.com/images/Elec...al%20Guide.pdf

Cheers,

Don

 

Hello Don,
Thank you for your reply.
The low beams on my car are H7 halogen/xenon bulbs. Whether these bulbs have an individual fuse? How I can find the fuse location/ the bad fuse?

I thought there will be one fuse for all four headlights. I found this electrical guide but it's hard to understand.

Kind regards,

 

Hi Anant,

It can be hard to interpret the electrical schematics if you haven't done it before. If you will look at Figure 8.1 on pdf page 87 of the manual, see the figures representing the headlamp units at the right side of the page. Find the rectangular figure for the RH headlamp unit.

The bulbs are represented by an X inside a circle. Find the symbol for the RH main bulb. The solid line that connects to the bulb and goes leftward to the Front Power Distribution Fuse Box (FPDFB) is the source of the 12V power to the bulb. The OG label above the wire indicates that its insulation is colored Orange with a Green tracer line.

The FPDFB is located in the front right corner of the engine compartment near the anti-lock brake modulation unit with several metal hydraulic pipes attached. Remove the lid of the FPDFB to reveal the fuses and relays.

The OG wire connects to Fuse 16 (20A) in the FPDFB, which provides power to both the left and right main beam bulbs, so we can assume there is nothing wrong with the fuse. However, between the fuse and the right main beam bulb is an electrical connector labeled EC35-4. That means the wire connects through terminal 4 in connector EC35.

If you refer to the previous page in the manual, pdf page 86, under the section labeled Connectors you'll find that EC35 is black in color and "8-way," or having 8 conductors (and up to 8 wires attached, though possibly fewer). Under the Location heading, this connector is part of the group located in the "Engine Compartment/RH Front." That is not very specific, but obviously this connector must be somewhere between the headlamp unit and the FPDFB where the fuse is located, and looking again at the schematic, the positioning of this connector on the dotted line indicating the FPDFB, you will probably find that this connector is on the underside of the FPDFB itself.

Fuse 16 receives its 12V power from the Main Beam Relay, R2 in the FPDFB, but again, since this fuse and relay also provide power to the left main beam bulb, we can assume the relay is functioning properly.

Since you don't seem to have 12V at the bulb connector, it does sound like your problem is on the power side of the circuit. But just to complete the diagnostic examination, the other side of the circuit is the ground.

The solid horizontal line that connects to the bulb and goes to the right is the ground wire. The "B" above this line indicates that the wire has Black colored insulation. The symbol of three lines of different lengths represents Earth or Ground. That ground point is numbered G3BR.

Now refer again to the previous page in the manual, pdf page 86. Under the section titled Grounds, find G3. It's location is given as "Engine Compartment/Below Front Power Distribution Fuse Box." That is a little vague, but the ground is one of two behind the right headlamp unit. You'll see two large nuts with several black wires connected to them.

A common problem with the headlamps is corrosion that develops on the aluminum nut, threaded stud and wire terminals. The aluminum oxide is a whitish compound that forms in a very thin layer, but it is an electrical insulator so it interferes with the flow of current.

Cleaning the grounds is well worth doing. The upper nut and stud are easy to access, but on our XJR the lower nut is difficult to remove and replace because there is very little clearance between the headlamp unit and the metal framework to which the ground studs are welded. The photos in the post at the link below show how I clean the ground studs, nuts and wire terminals. Also note that the torque specification for the nuts is a measly 6.5 ft. lbs., or just slightly more than hand tight. Several members have learned the hard way how easy it is to snap a threaded stud off of the body by overtightening the nut:

https://www.jaguarforums.com/forum/x...2/#post1156791

Please keep us informed.

Cheers,

Don

 

How about bulb grease on this stud after cleaning everything off. Any reason not to?

 

IMO a silicone dielectric grease will help. You want something that will seal out water but not negatively impact conductivity. Silicone dielectric grease gives you that and you can't tighten the nuts on the studs too tight as you might snap them off.

 

Dielectric grease after you have cleaned and reassembled everything is fine, but you don't want to apply it before reassembling the wire terminals and nut because dielectric grease is non-conductive. In fact, "dielectric" literally means a non-conducting substance or insulator. It works fine on bulb bases because the socket terminals scrape away enough grease to make contact with the bulb base, and the remaining grease insulates the connection and protects from water ingress. But on sensitive low-power sensor and logic circuits, adding any resistance at all can adversely effect performance. And since, with a ring terminal and nut connection, you have a "squashing" connection rather than a "scraping" connection, it is likely that a thin layer of grease will be trapped between the ring terminals and nut, potentially adding considerable resistance to the connection.

As an example of how sensitive some circuits are, if the resistance across the terminals of the engine coolant temperature sensor is 0.19 ohms, the ECM will understand the coolant temperature to be 212 degrees, or too hot. However, if the resistance is increased just 0.135 ohms, the ECM will understand the coolant temperature to be 176 degrees, or too cold. (Example from X308/AJ26 Engine Management System manual because I happened to look it up last night).

And as Sean says, please don't forget that very low torque spec for the ground nuts of 6.5 ft. lbs., or just slightly more than hand tight. Snapping a threaded stud off the aluminum framework will ruin your day.

Cheers,

Don

 

Yep, pardon me. Don is correct and I was thinking post assembly, just didn't say it. Thanks Don.

 

What keeps me glued to this forum is the technical knowledge and clear explanations of the how and why, not just the what. "Scraping vs. squashing" is clear as a bell.

Thanks!

 

Hello Don,

Thank you for the detailed explanation. Now, I can understand how the wiring is performed.

I have got all tools to perform the grounds cleaning and also new wiring harnesses. I have a few questions:

1. There are more than 1 wire attached to each nut, the aluminum oxide should affect all parts connected to that nut, right? I believe only passenger side light is not working.

2. After looking at the electrical connection, the crumbled connector contact might have tripped something between the fuse and the light connection. What do you think?

Kind regards,

 

Yes, the aluminum oxide forms on all the aluminum surfaces exposed to air, so you want to use a small wire brush to clean both sides of all the ring terminals, the flat of the nut and the threaded bore if you have a small wire brush that will fit, and the threaded stud. Flush all the parts with a zero-residue contact cleaner spray and allow them to dry before reassembling.

From your earlier description, I have understood that the electrical connector that crumbled was the one that connected to the H7 bulb. There is also an electrical connector for the entire lamp assembly. The 12V for the low beam bulb arrives on the Orange wire with Green tracer line (color code OG). If you do not find 12V between the OG wire and the Black ground wire (with the light switch on), then the problem is upstream. If you do find 12V, the problem may be in the wiring inside the lamp itself.

Don

 

It was a simple fix. The fuse was blown. I changed the electrical connectors on both low beam and also cleaned the ground. Thanks to Don for explaining the fig. 8.1 and suggestions.

I am hoping that now this will last another 10 years... ;-)

I found a compatible fuse- BP/ATC-20-RP.

Thanks.

 

Just found a new (to me) product at the electrical supply house, later also at my hardware store, GB brand Ox-Gard, anti-oxidant compound for use in older aluminum wire installations, to be applied and brushed in for maintaining "inter-strand and inter-conductive paths" among other attributes, like "improves conductivity". Seems like just the ticket for these ground studs. When I finally get the car on a hoist and get the bumper cover off so I can get all the headlight buckets shined up, new bulbs, new spring wire keeper installed, this will be on my list.

Gardner Bender ox-100B

 

It's probably fine to apply Ox-Gard to the exterior of ground points after you've cleaned them, reassembled and retightened the nuts, but I would strongly recommend against applying Ox-Gard or any other substance between the ring terminals, studs and nuts. There is no scientifically valid means by which Ox-Gard can improve the conductivity of a clean connection. Ox-Gard OX-100B contains graphite, talc and zinc powder, none of which is a better conductor than aluminum (aluminum is 3 times more conductive than zinc and something like 3 orders of magnitude more conductive than graphite (carbon)). Talc has very low conductivity.

Many of the critical sensor circuits are very sensitive to even minor added resistance, which can affect the interpretation of their signals by important control units like the ECM, TCM, etc., so it is best not to add any substance between electrical connectors for anything except high-current non-critical connections like light bulb bases.

Ox-Gard may be good for helping to seal out air and moisture that causes the formation of aluminum oxide, but dielectric grease is probably just as good and less expensive.

Cheers,

Don