LEDs actually operate on 3 volts. If you were to break the end LED off you would find a resistor underneath, in the center of it, that reduces the voltage. 12 volts in or 14 volts in wouldn't make much difference. ( I dont know how headlight relays could have any effect on dash lighting either.) This is a pretty large cavity for only 4 illumination bulbs. If you were testing while out in the sunlight with original #158 incandescent bulbs, you could hardly tell they came on. Any will appear brighter in the car, in the dark. New vehicles have a lot more lights, lighted needles, etc.., so they light up well in daylight. You would need more than the 4 bulbs to get that look from a classic instrument panel.