John---Quite a bit of light can be gained by cleaning off the bulbs.
Also the inside and outside lenses gather dust and a calcium-like
deposit over time. Most lens dirt will be inside, and lens removal is
called for to get at it. Easy enough to do, but go easy with the foam
gaskets. Replacements are available, should you want the best seal.
Polishing with a product like RAIN-X does a good job on the plastic
lenses, after blowing them clean. A multimeter could tell you if you're
getting at least 12V at the bulb area.
Dick
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