Most of the time, it's the contacts in the bulb socket, they are too far apart
for the LED wedge base, which is thinner. Both my reverse light socket
contacts needed pushed closer together, because the LEDs did not work.
They're in and working after the fix. I did my own LED bar for the trunk
light, because the assembly was missing...
For the trunk LED:
If you have the trim cover, take that off, let it hang by the "T" release cord.
Unplug the light harness, and take the lens assembly out.
Use an eyeglass type small screw driver, or dental tool, and push
side contacts in towards the center of the socket so they touch.
Plug the LED in the socket, then plug the harness back in. If the LED does
not light, reverse it. If it does not light again, then it's the LED.
Once the LED is confirmed working, put it all back together.
Walmart has these LEDs, just not in green, but have White (6000k), Red,
Blue and Amber. They are $6.88 a piece, and they are bright. I use them,
and so far have a set that's lasted 2+ years in my Jetta headlamp "City"
You can still push the contacts in on the festoon socket. There are
two metal tabs, one on each end. Push them in towards the center
so the LED tightly fits.
Also, make sure the thing works... Apply voltage and ground directly
to the LED to be sure it even works. They are polarized, so if it did not
work the 1st time, rotate the LED and try again. If you get no light with
direct 12V power, then the LED is bad.
ALSO, depending on where you got that LED, they suck. There is a
wire that is soldered to each end cap, and they come loose. I bought
a set brand new for another application, and the wire poked through
the end of the CAP, and made intermittent contact. Had to solder the
wire in place again.
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