My High Mounted brake light in my 2002 X-Type is only working on occasion. Any ideas on the cause? All the LEDs light up when it works and the regular lights work normally. It seems to be more of a problem in cooler weather.

 

JDP, I would check at the plug and see what you have there and then see if it is a wiring issue or a light assembly issue. SHould only have 2 wires going to the 3rd brake light. If you get 12 VDC there when you apply the brakes, the problem lies in the light assembly.

I will look at the electrical diagrams when I get home.

 

JDP, if your taillight stop lights are working, then you should have power to the 3rd brake light. Please keep in mind that the 3rd brake light is grounded right near the light. So, when measuring the power to the light, measure from the orange/green wire to any metal part of the body. Then switch the multimeter over to resistance and measure continuity from the black wire in the plug to chassis ground. If you don't have 12 VDC, then you have a bad wire running from the split for the brake lights to the plug to the 3rd brake light. Hand over hand the wiring and see what you find. Fix the spot that appears to make a sharp angle (wire broken internally). If the continuity check of the black wire shows a high resistance (anything over 5 ohms), then you need to follow the ground wire and see where that has been damaged and fix that. if the orange/green wire is good and the ground wire has good continuity, then your problem is the 3rd brake light housing. Odds are, unless you can see the issue, replacing the 3rd brake light is going to be the easiest/cheapest thing to do.

 

How can I best find the wiring? I don't know where to start looking. Do I need to pull down the headliner?

 

JDP, yes, you are going to need to get in under the headligher and see what you can do about access the 3rd brake light. I wish there was an easier way of doing this, but that is about as easy as it is going to get.

 

Just a quick update, last Friday my battery died, and I replaced it, since then the light has been working properly. I hope it will stay that way.

 

JDP, because those lights are LED, it is very possible that you car's electrical system was running low on voltage and that will cause LEDs not to function properly. Keep an eye on it and if you have future problems, do what I said above.