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2005 Deville DHS - Third Brake Light not working

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Recently joined the family of Cadillac Owners again,  this car rides like no other,  I did find a few issues to work, one being the third brake like not getting power.  I have ordered a new used light, but in testing the wire plug under the liner on the deck lid I do not see where it's getting power with the key turned on and then brake pedal depressed enough to light up the left and right brake lights.  Check the fuse under the hood, 16 or 19, but they seems fine, check the all the fuses under the back seat but didn't find any out. Didn't see crimped wire but will look more for more soon. Is there a relay somewhere I should be checking?  Or any other advice.
This is a high mileage but well cared for car.    

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If there is no power to the third brake light and the other two operate properly, there must be a broken wire in the harness to the third light. 

'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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It should be noted on the Deville....there is a different fuse for each tail light.

All fuses should be in the rear underseat fuse block.

Third stop....#19...'STOP LP' fuse.

Right tail...#10...'LP PK R' fuse.

Left tail...#23...'LP PK L' fuse.


The fuses are also not side by side in the fuse block. They are scattered around the fuse block with no logic to placement.


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Checked the fuse #19 and it's good so the issue of no power at the plug in, to the light must be a wiring issue.

Well the ebay replacement Third break light doesn't appear to work.  Is the third break light twelve volts?  There is a plug in with a white and black wire in it.  I assume it's 12-volts.    


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It's 12v.

The wires can break in the trunk lid harness near where the trunk hinge is....where the harness flexes when opening and closing the trunk lid. 

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Thanks Logan,  I in fact figured out that the original light and replacement light do infact work.  The White wire is positive with the black being ground.  I was testing them backwards.

I have spliced the wire the light side of the plug to test the power and ground.  Sure enough the Power (white) wire is not sending power to the light. The black(Ground) is sending a ground to the light.  I used a battery jumper box to connect power to the white wire and ran the ground of the battery box to the car and the light works.  So the short story is yes the power wire is either severed somewhere or the power wire is not getting power from the fuse box.  But the ground is.

I will be digging some more tonight.  Thanks for the help.

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  • 2 years later...

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