Headlight relay install You Gatta do it.

[Russell]

Originally Posted by KEH

Percentage of full light output at various voltages, with 12.6 volts being "100%" :

12.6v = 100%
11.5v = 75%
10.3v = 50%
8.7v = 25%

This is all very true, but remember that your truck operates at 14.9 - 15 volts with a properly operating alternator. So, you'd actually wind up getting about 11.3 volts at the headlights, using the same ratio of 9.5 volts at the lights when operating at 12.5 volts.

So, that number puts you at about 75% lighting -- Using a relay install, you drop your losses to about .4 volts or so, according to your information. That means that with a relay harness, and a properly operating alternator, you could very well be getting over 14 volts straight to your headlights. Thats why this makes such a phenominal difference in lighting. Its like overclocking your lights!