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

[Johntpr]

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.

 

[Xcentric]

Park lamp relay in the Smart Junction Box?

What is the battery voltage?

 

[shelbyelite]

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

 

[GTJack]

I had the same problem a couple of years ago just before my battery died. It was on a charger regularly but it seems they have a limited life.

 

[junior]

I suspect a new battery is in order, good luck !

 

[Johntpr]

Thanks everyone. I ordered a new battery and will hope for the best !

 

[2112]

Subscribing to hear solution.

 

[Johntpr]

Well, Not having much luck. Today I installed a brand new fully charged battery, and even added another negative ground cable to the Oddessy battery.

No change, turn car off, and slowly, the left rear tail light will glow and come on dimly and stay on dimly. No other lights will be on.

I'm running out of ideas. Can anyone else think of anything?

 

[twobjshelbys]

Do the lights operate normally when you test them, ie, brakes, flashers, signals (compare side to side).

Also, while it is in glow mode, try pulling the fuse/relay for those particular lights (look in the owners manual, most likely the right one is in the Smart Junction Box under the passenger foot area). Does it still glow? If so, then some other hot line has shorted to it.

 

[FENZO]

I'm not looking at my car so I don't know if this is possible, but can you look at the light and tell if it is the reversing lamp, park lamp, or stop/turn lamp? Or can you get to a connector? You could follow it with a multimeter.

Do you have the wiring diagram book? Did you try to unplug the smart junction box? Start pulling fuses? You mentioned 18, in my book F1.18 is for the low beam relay of the right headlamp and F2.18 is interior lighting.

Fuses to try:
F1.1 , 2, and 3 are the smart junction box
F1.6 is the rear window defrost, park lamps.
F2.6 is the brake pedal position switch and brake pressure switch.
F2.3 is the park lamps.
F2.29 is the reversing lamps.
C2059 is the park lamp relay in the smart junction box.
C1007 is the fog lamp relay in the aux relay box.

Troubleshoot man, troubleshoot.

 

[Johntpr]

It seems to be a dim version of the parking light that stays on. All other lights work normally, and when car is running, all lights, hazards, brake lights etc work normally. When I pull fuse number 18 from the smart junction box, the light goes out.

 

[FENZO]

I'd pick up one of these.. my manual is a 2005, there may be small differences.

http://www.ebay.com/itm/2006-Ford-GT-Wiring-Diagrams-manual-/282427030038?hash=item41c1f67a16:g:F8gAAOSwAKxWV1yZ&vxp=mtr

 

[Johntpr]

I do have a 2006 GT shop manual and also the separate wiring diagram manual. Just not great at interpreting the wiring diagrams.

 

[KJRGT]

Bad fuse? Bad connection in the box?

 

[Johntpr]

Today I removed the smart junction box far enough to swap out the parking lamp relay using a mirror etc to access the back side. As a bonus, my hands are nice and bloody now.

Ugghh. Same problem, no change.

 

[Xcentric]

 

[FENZO]

Here's a way to determine if the power is coming from the source at the junction box or somewhere along the harness. With the car off none of the wires to the tail light should have voltage. This should help narrow it down.

Take the connector off the left tail light, connector C412.



Now test each socket on the cable side with a test light or a multimeter to see where the power is coming from. Also check continuity with ground.



Once you know that, check to determine if it is coming from the source or somewhere in between. If the power was on connector C412 socket.....

A - check pin/socket 19 & 14 of connector C2280c
B - check pin/socket 10 on C2280c
C - check pin/socket 28 on C2280e
D - ground. N/A.
E - pin/socket 6 of 2280c.

 

[twobjshelbys]

OK, so the diagrams above are a good tool. But it reminded me of another test. With the tail light fuse (relay?) installed, try removing other fuses/relays one at a time until it goes out. If there is a crossover somewhere that will help tell the source. Then the wiring diagrams above will help find where they might be crossed. Note: There aren't too many things that have power when the ignition is "off".

Hmmm... The "hazard" blinker is one that would have power at all times. Have you tried toggling that switch to see if things change?

 

[Johntpr]

As a quck update, so far, pins C and E both show voltage on the left tailight plug. Not enough to light up test light, but enough to show on multi meter. I will keep following your charts. I also am wondering if the turn signal switch may be causing issue but it seems to function normally. Those pins showing voltage on the tailight wiring plug are the left turn signal feed and the lamp failure circuit feed. More testing to follow.....

Toggling hazard switch didnt help. Pulling fuse 18 turns off the light.

Also, large connectors c2280e and c2280c are on the reverse side of the smart junction box and will be a joy to access for testing purposes. Why is nothing ever easy?

 

[twobjshelbys]

As a quck update, so far, pins C and E both show voltage on the left tailight plug. Not enough to light up test light, but enough to show on multi meter. I will keep following your charts. I also am wondering if the turn signal switch may be causing issue. Those pins on the tailight plug are the left turn signal feed and the lamp failure circuit feed. More testing to follow.....

Toggling hazard switch didnt help. Pulling fuse 18 turns off the light.

Did the flashers go on without the key in the on position?

Right, that's the main circuit for that lamp. Pulling the other ones will point to the one that is crossed.