tail light intermittent

Dmflash

Original poster
Member
Dec 16, 2021
22
Canada
Hello, I have an 07 Trailblazer with a passenger side tail light issue where it wont come on until the transmission is shifted into drive (driver side is illuminated while in park) . I had the truck undercoated with rust check a few days before and all of the grounds attached to the frame are coated in oil, could this cause such a weird electrical issue?
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I had the truck undercoated with rust check a few days before and all of the grounds attached to the frame are coated in oil, could this cause such a weird electrical issue?
I doubt it. I would double check the grounds. Maybe when you put it in drive, it momentarily turns on the reverse light and maybe sparks the ground. Check power outputs at the taillight connector. If those check out, I would suspect the taillight circuit board. When checking for power and ground, use a load, like an light bulb, to check that the circuit can carry an actual load.
 
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Redbeard

Member
Jan 26, 2013
3,466
I had an '04 trailblazer. When mine went out it was both a ground problem plus the circuit board for the tail lights. The circuit board I picked up through ebay for about $15 (and they were a/c delco) and it was straight forward to change out. This was probably 5-7 years ago. For the ground I ran a new ground wire straight to the frame (seem to recall drilling a new hole for the screw). I would suggest picking up some dielectric grease for the bulbs cause there wasn't any on mine when I changed them out. Check out Amazon and Rockauto for pricing.
 

flyboy2610

Member
Aug 24, 2021
460
Lincoln, Ne.
Bad grounds can cause all kinds of weird electrical issues.
Given that you recently had the vehicle undercoated, checking the grounds would be my first suggestion.
 

Dmflash

Original poster
Member
Dec 16, 2021
22
Canada
Yeah I think I might have to clean off all the grounds and go from there . Coming home from work my heated seat came on by itself along with the taillight problem. I would of thought the oil would be beneficial for the ground connection as they were pretty rusty .
 

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