I agree with Gdetrailer, it is hard to make suggestions without knowing what the fixture looks like. There are a lot of places to buy LED bulbs and it is easy to wire them. All of the strips I have purchased were marked with the polarity. I have used the film type strips that generally come in 5 meter spools and I have used the aluminum backed strips 0.5 meters long.
The wire size can easily be as small as AWG 18. If you are looking for a corncob with a A19(Edison) base in 12v, that is a little harder, anything used in vehicles is easy to find.
Any fixture that has the base of the bulb down will require a higher lumin rating than LED that are pointing down. Also LEDs come with and without lenses, in different Kelvin ratings and different angle of disbursement.
I buy all my LED strips on eBay and have only had one failure and that was a 12" amber waterproof strip. I have been using a 5 meter strip cut down to 9' in my kitchen of the S&B for about 5 years. I had one touch pad dimmer fail but none of the LEDs.
I have been wiring strips and power cords since I started making my own fixtures for two reasons, first they are easy to solder and I think better and second, they don't take up any room. I've been soldering electrical and electronic components for over 63 years and I find it more secure.
It is really easy to rewire fixtures to accept LEDs once you know what style bulb you are going to use and hook the bases up.
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David Bishop
2002 Winnebago Adventurer 32V
2009 GMC Canyon
Roadmaster 5000
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