What myself and others tend to use for passenger car lighting is strip leds size 3528 with 3 leds per 2" length. Warm white seems to produce the most realistic lighting. They are commonly available in 5m or 10m reels in 12vdc voltage range. AliExpress or ebay are good sources. Domestically Amazon has them also.
For connectors I have found JST-PH 1.25 work quite well. They are available on ebay in lots of 20 each male and female, for under $2. I buy about 4 or 5 lots at a time, usually with all shipped for the same cost as 1 lot would be. The header pin pitch is 0.1" on the board so you can also use any header you like including JST XH or JST EH, or Dupont pin headers, as well as others. What I do is solder the wires of the small 1.25 headers above directly to the board, then the mating end gets soldered to end of the led strip. This way the strip can be easily disconnected for car maintenance anytime. For the ac power supply side I just cut off the wires that supply the original lighting and solder them directly to the board.
16" cars can usually accomodate a strip 14" long, so 7 sections, 21 leds total. 18" cars use a 16" strip 24 leds, and 21" cars use an 18" strip 27 leds.
hope that helps,
Rod
