I think I'm the original blue LED modder.
LEDs do not require a specific voltage, they require a specific current. That's why the additional resistors are 'current-limiting' resistors. They have electrical properties quite different from a normal light bulb.
The door panels have a custom size of LED that I didn't easily find anywhere. You can take a 3mm mini-LED, and sand or clip off the ridge around the base so the LED will fit in the hole where the original LED was. Also note that LEDs are
diodes, and power only goes through one way; if you wire them up backwards, they won't illuminate.
The door switches have resistors (about 300 ohms if I remember right) that are correct for the amber LEDs that are there. The blue LEDs will have a different current draw and need a different current-limiting resistor value. Since they are based on different technology than the old red/green/yellow LEDs they will glow much too bright and burn out themselves or burn out the old resistors. I think I replaced them with about 4k resistors to get them to glow with the right brightness. You really should have them very dim, so they don't distract when you are driving, just enough glow to show the button in the dark.
I got a bag of 100 LEDs on ebay from Taiwan for cheap. They were almost certainly 'rejects' because they were wildly different values, and I had to test them all to measure the current draw and evaluate how bright they were and bin them by brightness.
