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Discussion Starter #1
I'm having a weird issue with my license plate lights. I looked up the number for the bulb (C-5W) in the manual. Couldn't find that in the store so got a same size 5W festoon base bulb (Sylvania 6418). According to AutoZone they are the correct cross-reference for the C-5W. My holders were corroded so I took them loose and cleaned em up. Checked the bulbs and read 3.5 ohms. In the holders, 3.6 ohms. BULBS AND HOLDERS GOOD The terminals on the car are reading 9.5V with engine off and 11.8V with it on. PROPER VOLTAGE Plugged the holder back up and get no light. Take bulbs out and read 11.8 at terminals of both holders. Can't figure out why lights aren't working. Anyone??
 

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Meh.
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If they are LED's, flip the bulbs around.

If not, you probably still have corrosion on the holders. They are very nasty for that.
 

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Discussion Starter #3
Not LEDs. Cleaned holders well (Washed all and sanded contact points). Tried something else: with test leads between battery terminals and holder terminals, I get light. So, it has to be something from car, but leads from car are reading proper voltage. Still at a loss...
 

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2006 ZX5 2.0, 2004 ZX3 SVT EE. 2004 ZX3 SVT
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If this is a hatchback try moving the hatch up and down while checking voltage and look for a change. The wiring harness can go bad from opening and closing the hatch.
 

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Discussion Starter #5
There was a white plastic cover over one wire to each side and black shrink tubing over other. Cut both off and lights work now. Don't get it but problem seems solved.
"She falls down a well, her eyes go crossed. She gets kicked by a mule, they go back. I don't know."
 

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That sounds like the typical issue of fixed now and tomorrow not working again. I've been through that before on those lights.

The bulb type is one that if you keep installing and removing the bulbs the bulb itself goes bad as nothing holds the end caps on except a minuscule drop of solder so small you can't hardly see it. The rolling in and out of the bulb into the sockets twists the solder point loose. Then they work perfect until first bump hit and they quit.

Sanding contacts there doesn't do spit. Throw the assembly into salt and vinegar water to remove ALL corrosion in 5 minutes and then plastic wirebrush all of the contacts and it also will remove any corrosion deposits dropped into bottom of lens too to add about 200% more light output.

Turn them back on and you WILL get a surprise.
 
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