First step is to figure out how to gain access to the light bulbs. Once you’ve done that, have each one checked to see if it’s burned out.
There are three ways to do that; a visual inspection, (if it’s very dark inside the bulb, it’s either blown or about to be), second, if you have good eyes, or very myopic ones, you may be able to verify that the filament is still intact, (the tiny little wire inside that gets really, really hot!),
and third, you can use an electrical meter to check for continuity. Of course you have to have one, and know how to use it.
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Next, if your bulbs are okay, test the various functions, turn signals, parking lights, and brake lights. One way to do this, even alone, is to use a reflective surface. A strip-mall store window works great for this. Just back up in front of the window, and look in the glass for your reflection. Test all the lights and verify their function.
In the absence of reflective glass, you can use a more ordinary surface, such as a garage door. Close enough to it, and dark enough, you should easily see each light and its proper operation.
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That’s about it, except if something doesn’t work, like brake lights. Then you have to fix whatever’s wrong.
Bingo. On the left.