This is my first post asking about a problem, but this site is so responsive to these types of things that I'm hoping for help.

My 2004 XK8 driver's side bulb was out. I checked the fuse and it was blown. I replaced the fuse and it blew immediately when the lights were turned on.

I removed the low beam bulb and it was blown. Without the bulb in, the fuse would still blow when the lights were turned on.

I don't want to put a new expensive bulb in without finding out what the problem is. Has anyone had this type of issue?

Many thanks for any suggestions. Richard

 

Hi Richard, just saw your note, let me try to help.

What we know:
Fuse blows without bulb installed. This says there is a short somewhere between the hot wire to the bulb and the switch to turn on headlights.

If this was not true I'd ask you to verify/validate fuse rating. That's moot since no current should flow with no bulb.

How to troubleshoot:

1) take digital meter to bulb socket. Place probes on each wire in socket. Measure continuity. Does meter beep saying the two wires are functionally connected?

Yes: now measure ohms same connection. Note reading. This says your hot lead is "grounded" just like we suspected. One bulb wire is hot through the switch, the other is grounded.

The ohms reading is little more than anecdotal but if you see a high reading, more than say 20 ohms it tells you the short is high resistance, or very far away.

No: either the wire is open to the socket (wire broken somewhere and it's exposed end shorts); or your car has high voltage xenon lights. Technically you can have a defective switch, but let's look at wires first.

If xenon, I'd sacrifice a fuse. Locate the transformer box that takes 12 volts to 20,000 volts for the light to energize. Disconnect the 12 volt wire into it. Replace fuse, see if it blows.

Side bar:As I type I realize more conservative mechanics would measure this 12 volt wire to ground (ohms) to first ensure there is no short, but I've seen unenergized hot wires show ground, and if you do find ground in this scenario you'll be measuring the same thing on the other working side. With a proper fuse your risk is insignificant imo.

Did fuse blow? No, you have defective transformer. Yes, short proven to be in wire or switch before this connection.

If short is between switch and bulb, I'd get wire diagram and locate connectors between the switch and the bulb. Disconnect to isolate where the wire is grounded.

If possible disconnect the connector closest to switch first. We want to eliminate the switch.

How can you do this without burning a lot of fuses? Get hold of a test light. Plug it into fuse location for tests. Since you know you can put this light across the battery terminals, you know it doesn't create an unsafe situation.

John

 

John,
I really appreciate your comprehensive step-by-step plans to track down the problem. I will followup on your suggestions and I will let you know what I find.

I have one question before I start: I have HID - D1S bulbs and I am not sure what or where a 'transformer' would be located. Would there be any merit to the first thing is to try to locating the 'transformer box' and disconnect the 12 volt wire to it, replace the fuse and see if it blows?.... (and how it doesn't!)

I have seen references to Ballasts, Transformers and Control Units and am not sure what-is-what.....

Any suggestion would be appreciated! Richard

 

Richard I have a 98, so flying blind with your year. Maybe someone familiar can advise where the transformer is located?

From your description of the bulb, yes you will have a ballast. We need to locate it for a quick test.

I am sure someone will jump in to help

John

John

 

John

Thanks again for your response. You are helping me immensely as I am starting to understand where to start and what may follow on the search for a solution. I think the bulb itself has an 'ignitor' as part of its base..... at least in a thread somewhere it was described that way.

is that 'ignitor' also considered a transformer? Or a Condenser? Or a Control.. ?

I really am not sure how these words are used when dealing with the headlights..... I'm hoping to get some insight into this whole thing.



Richard

 

Yes the ignite is a descriptive term. These bulbs use xenon gas, which when energized with a bust of high voltage emits light.

Quick description of the terms:

Transformer: converts incoming voltage to higher voltage, not great for high current needs.

Ballast- guess I think of it like a capacitor transformer mix. It provides a stable resiviour of voltage current. Also used in just about any fluorescent light around the house. When that lite flickers, ballast is bad. No longer supplies stable supply.

Your xenon lite needs burst of high voltage to get started, than steady current to continue without flicker.

Condenser - old name for capacitor. Stores electric charge and blocks dc. While it too provides a resiviour, it provides a less stable flow than a ballast. Has other uses but unrelated to your wuestion.

John

 

Again, John, thanks for the info. I'm starting to check things out this pm.... we'll see ...
Rich