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Discussion Starter #1
The center brake light on my '05 Elise is partially dimly lit when the ignition is turned on (approx 3 V current). Thinking the main brake switch is bad, I disconnected it - to no effect. It's driving me nuts. Any thoughts as to what I should check next? I searched the entire Forum, but couldn't find another thread around the same problem. Here is a pic:
 

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Discussion Starter #2
It's been a while since I originally posted this thread. I was hoping to trigger a few thoughts or replies, but unfortunately didn't get any reply from anyone out there. A slight correction, though: the weak current I detected in the circuit was closer to 5 volts (not 3 v).

Meanwhile, I took a closer look at the wring diagram (which to me is pretty confusing). I decided to open the fuse box (under the right front outside panel) and pulled the 10 amp ABS fuse. Lo & behold the partially lit center brake light went off, but all other stop light functions remained intact. Obviously, now the ABS warning light in the instrument cluster came on. Since I'm not a vehicle electrician and am fishing for answers, could it be that one of the ABS sensors or connectors at the wheels might be bad? I appreciate any input. Thanks!
 

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Thats really odd. If it was me, I'd study the diagram like you did, and go nuts with a multimeter. Have you tested to see if the voltage is present at the brake lights that are in the actual tail lights? If its a problem on the positive side of the light, the tail lights should also be getting the 5v as they share the same positive wire. I love chasing problems like this, I find it fun.

I wouldn't think it would have anything to do with the wheel speed sensors, but then again I guess you can't completely rule it out. I'd put the fuse back in, and find the wire at the abs unit, which it looks like SHOULD be green with a purple stripe, and see if you have 5v coming out of the abs unit. There are also 2 black wires coming out of the abs unit which are both grounds for the unit, I'd make sure they have clean grounds.
 

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Discussion Starter #4
Yes, the 5V current is measurable at all brake light sockets. As I mentioned before, once I pull fuse #F12 (which ties into the ABS module) the current noise stops, but the ABS CEL come and stays on.

Are there any experts out there that can tell me if I can repair this malfunction or do I have to replace the ABS module? I researched the entire Forum, but couldn't find anyone else reporting on the same problem. Any suggestion is much appreciated!

Below is a link to the complete wiring diagram. Please take a look at page 17 (sheet 16) for the fuse info and page 15 (sheet 14) for the ABS schematics.

http://http://www.boefabrication.com/downloads/elise_north_america_1-16.pdf
 

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Discussion Starter #5
Partially lit 3rd brake light, code P0171, aftermarket LED tail/brake light bulbs

Ok, it's been quite a while since my partially lit 3rd brake light issue arose. I exhausted all my amateurish probing months ago and flatly ignored the issue since everything else on the car seemed to be working just fine.
Until recently, that is. All of a sudden the old P0171 code ("Bank 1 too lean ...") kept popping up. I replaced the MAF sensor, but didn't replace the O2-sensor. Whenever I had the CEL & fault code extinguished, it popped right up again. I finally got so frustrated that I retracked meticulously any change I had made to the car over the last year. One of the things I had done, was replacing the tail & brake light plus turns signal filament bulbs with aftermarket LED bulbs (bought off Ebay ...). Mind you, my Elise is an '05 model which didn't have any factory installed LED lights. I know what you are thinking, but I did have the recommended load restrictors installed in the brake & tail light circuits. When I changed the turn signals I switched to a LED flasher unit which worked perfectly without any load inline restrictors. If memory serves me right, the first time the CEL came on with said P0171 fault code was shortly after I had replaced the brake lights and pretty much also around the time when the partially lit 3rd brake light came on.
So a couple of days ago, I took all LED bulbs out of the tail/brake lights, but left the LED amber bulbs at the front untouched. I fired up the car and to my surprise no more lit CEL. Neither is the 3rd brake light partially lit anymore. I did not use any OBDII scan tool to reset & extinguish the fault code this time. So I drove the car more or less hard for maybe 40, 50 miles with a few stops in between and switched of the ignition a few times along the way. No more fault codes. I had a smog check done today and it passed with flying colors.
Here is my question: Does anybody out there think the LED bulbs were triggering the fault code and tripped the CEL? Or was it just a pure coincidence? A friend of mine who knows a ton about vehicle electronics thinks the LED bulbs, especially with the load restrictors installed, should have nothing to do with triggering the fault codes. Has anyone out there had any similar issues? I'd love to hear from you.
 
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