Left / Driver's side Tail light Issue - comes on dimly by itself


KJRGT

GT Owner
Mark II Lifetime
May 4, 2006
2,840
SoCal
if nothing else works I know the number to a good exorcist
That is funny!

Not so with the issue at hand. Best of luck. You will prevail.
 

PL510*Jeff

Well-known member
Mark IV Lifetime
Le Mans 2010 Supporter
Nov 3, 2005
4,628
Renton, Washington
Great news!
Yes it is. Lingering in my mind is why the taillight turned on.
 

NorthwoodGT

GT Owner
Jun 12, 2009
1,100
Michigan
just my opinion but I seriously doubt it's the smart junction box (GEM module). I would change all the relays in it before I'd change out the box.
 

Johntpr

GT Owner
Jan 18, 2017
141
Rockland County, NY
just my opinion but I seriously doubt it's the smart junction box (GEM module). I would change all the relays in it before I'd change out the box.
Did that...changed relays....no luck. Traced all the wiring at every connector up to the smart junction box...don't know what else it could be besides the smart junction box.
 

Johntpr

GT Owner
Jan 18, 2017
141
Rockland County, NY
2006 GT

Left / Driver's tail light will dimly come on by itself when car is off. You can use remote, lock car, and all lights will go off. Slowly,the left rear tail light will glow and come on dimly and stay on dimly. No other lights will be on. Not on battery tender when this is happening.

Fixes tried so far:

1. Cleaned negative battery cable/terminals and ground bolts/ frame surfaces. Checked battery voltage
2. Cleaned rear tail light harness grounds on both sides of rear chassis
3. Cleaned under dash lighting harness ground
4. Pulled brake light switch wiring to see if that turned off tail light - no luck
5. Pulling 15 amp fuse # 18 for the lighting service does turn off the tail light, so the issue is in that circuit I would think..just can't figure out where.
6. Disconnected rear view mirror wiring...nothing changed
7. Cleaned electrical connectors to tail lights themselves

Anyone had this happen to them or can suggest any other ideas to investigate? I'm stumped.

Thanks in advance.
 
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Xcentric

GT Owner
Mark II Lifetime
Jul 9, 2012
5,210
Myakka City, Florida
Park lamp relay in the Smart Junction Box?

What is the battery voltage?
 
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PL510*Jeff

Well-known member
Mark IV Lifetime
Le Mans 2010 Supporter
Nov 3, 2005
4,628
Renton, Washington
Oh no. Start with obvious first, battery condition, battery ground cable where it meets the frame etc.

In my case, I am waiting on a new smart junction box.
Update..light is now off. Had my son put the battery charger on, and within 2 minutes the light turned off.

GT's do weird things when the electrical supply is poor. Odd that the SJB, with low battery voltage,(Longest non driven period in 11 years! would cause the non key operated tail/parking light to turn on with a glow. In my case it was on the right and johnpr's was on the left.

In my case the GT was parked for 6+ months. (Btw longest non driven period in 11 years!) Not on tender. Battery was flat. This was two weeks ago. Using the advise of our GT Guru - aka Rich Brooks - we put the charger on at a 2amp setting for two hours. The unplugged it for 2 hours. Repeated three times. No issues - gauges all worked correctly - didn't lose data so passed the required emissions check for license renewal.

Drove it everyday for the next week. Only thing I noticed that was odd - when key was turned on the gauges were a little tardy in being initialized, odometer was the last to come alive. It took maybe 30-40 seconds to activate all of them. I have always waited to push the start button until all gauges were powered up. Over the period of that week of driving I put on nearly 600 miles. No issues - other than slow gauge activation. Battery is less than 3 years old.

So this morning my son put the charger on again for two hours. And gauges and OD were all initialized in just a few seconds.

The tail/parking light issue is gone but it will be interesting to discover why low battery would cause a led twilight to turn "itself" on.

Bill Dickey - Anlogdesigner - Two Shelby - or any of you ee guys on the forum are hereby challenged to sort through all of this and hopefully find a final solution.
 

shelbyelite

PERMANENTLY BANNED
May 10, 2007
1
Ive also seen this happen when the battery is getting low and / or the ground on the battery cable is not getting a good connection to the frame
 

paul b

GT Owner
Nov 2, 2006
810
Not much help, but many times an energized or bad ground circuit causes a dim light to glow when it shouldn't. Can you get to the light socket and test the ground?
 

twobjshelbys

GT Owner
Jul 26, 2010
5,170
Las Vegas, NV
Bill Dickey - Anlogdesigner - Two Shelby - or any of you ee guys on the forum are hereby challenged to sort through all of this and hopefully find a final solution.
I think the original poster said he has already replaced the battery and checked the ground. However, he didn't say if he had brushed it around the cable ring to remove paint to get a good ground.

I really don't think it is the SJB causing his problem but I guess we'll see.
 

Johntpr

GT Owner
Jan 18, 2017
141
Rockland County, NY
Not much help, but many times an energized or bad ground circuit causes a dim light to glow when it shouldn't. Can you get to the light socket and test the ground?
yes, tested/cleaned all the grounds. Light socket ground OK ..just has voltage coming from left turn signal feed and bulb failure feed. Looking more and more like a smart junction box circuit board or other internal failure.
 

Johntpr

GT Owner
Jan 18, 2017
141
Rockland County, NY
I think the original poster said he has already replaced the battery and checked the ground. However, he didn't say if he had brushed it around the cable ring to remove paint to get a good ground.

I really don't think it is the SJB causing his problem but I guess we'll see.
Yes, i ground down the paint around the cable ring, and even added another ground wire to the battery. New oddessy battery in place with proper voltage output.
 

PL510*Jeff

Well-known member
Mark IV Lifetime
Le Mans 2010 Supporter
Nov 3, 2005
4,628
Renton, Washington
I think the original poster said he has already replaced the battery and checked the ground. However, he didn't say if he had brushed it around the cable ring to remove paint to get a good ground.

I really don't think it is the SJB causing his problem but I guess we'll see.
Yes the SJB may be the issue as everything seems to go through it. While my light problem is "gone" for now, it would be good to know what the root cause may be. Nothing in my automotive experience can explain a light turning on when the car is parked and unattended. Sticky switch? Circuit jumping? Moisture/corrosion? A physical reason that is so far undiscovered and thus my hope is to find an explainable solution.
 

NorthwoodGT

GT Owner
Jun 12, 2009
1,100
Michigan
wow that's good to know. and yes, getting the smart junction box in and out is a real pleasure. I was going to tell you to save the relays out of the old one but there again, maybe you shouldn't. I currently am getting a clicking noise in my junction box when the A/C is on. only the A/C is generating the noise. there again, a relay going bad?
 

Johntpr

GT Owner
Jan 18, 2017
141
Rockland County, NY
wow that's good to know. and yes, getting the smart junction box in and out is a real pleasure. I was going to tell you to save the relays out of the old one but there again, maybe you shouldn't. I currently am getting a clicking noise in my junction box when the A/C is on. only the A/C is generating the noise. there again, a relay going bad?
You sure it's not coming from the relay box box under the hood? That's where the A/C relay is. Is the A/C blowing cold? Maybe a low borderline charge keeps the relay trying on and off to engage the compressor clutch.

Yes, I will save my old smart junction box. Hopefully, in the future, they can be repaired. The new SJB comes with 2 new keychain remotes. They are matched to the new SJB.
 

twobjshelbys

GT Owner
Jul 26, 2010
5,170
Las Vegas, NV
Yes, i ground down the paint around the cable ring, and even added another ground wire to the battery. New oddessy battery in place with proper voltage output.
So have you tried pulling the other fuses/relays to see if any other one is related? Note there is a fuse box in the trunk area too.

Also, you said you pulled the fuse/relay, but did you try swapping it with one of the same size?
 
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twobjshelbys

GT Owner
Jul 26, 2010
5,170
Las Vegas, NV
Did you try to swap bulbs left to right?
 

NorthwoodGT

GT Owner
Jun 12, 2009
1,100
Michigan
You sure it's not coming from the relay box box under the hood? That's where the A/C relay is. Is the A/C blowing cold? Maybe a low borderline charge keeps the relay trying on and off to engage the compressor clutch.

Yes, I will save my old smart junction box. Hopefully, in the future, they can be repaired. The new SJB comes with 2 new keychain remotes. They are matched to the new SJB.
you are correct. the key fobs supplied have to be used with the matching smart junction box. been there, done that. no, the clicking noise is coming from the smart junction box. has to be a relay going bad. everything works fine including the A/C blows cold.
 

Johntpr

GT Owner
Jan 18, 2017
141
Rockland County, NY
Did you try to swap bulbs left to right?
Well, the issue is there is voltage going through harness back to left tailight when the car is off. The rear tailights are LED and have no traditional bulbs.
 

twobjshelbys

GT Owner
Jul 26, 2010
5,170
Las Vegas, NV
OK, what I was looking for is that you stated there was power on the bulb failure line. Check the other side to see if that line is hot on the other side. It's possible that that particular line passes through the voltage through the lamps and if it goes open signals the failure (ie, a negative true)