Rigid High/Low LED's

LED's don't care about voltage so much... It takes a certain amount to fire them, then a certain amount to blow them, but anything in between will work.. the lower voltage is dimmer, the higher is brighter. You can go get a variable resistor from radio shack or a dimmer light switch from the hardware store and do the same thing. For what it's worth, you can also 'overdrive' halogen bulbs for more lumens, but at cost of shorter life and ease of blowing.. you can push a 325luman bulb rated at 12vdc to 450 or so by pushing 14vdc to it...

Anyway, your fogs go out when high beams come on because most state laws consider high beams two extra lights. Most state laws allow only a total of four drive lights on front of vehicle, so they are wired from factory to do what they do. Change that at your own risk.. it's done, and done often... I've never heard of a cop nailing anyone for it, or an inspection station issueing an infraction because of it, but by the letter it is illegal in most states.

Right now I'm looking at top racks for my rig, and I'll have light all around.. I plan on using a lightbar and HID spots on front.. led has light wash all over HID, but nowhere near the throw of HID. I'm going to get clever with this setup, though, and charge it from an aux battery pack I have mounted in my bed which is charged both through a 12vdc trickle tied into the main batteries, but also a solar panel on top of the camper shell.. the trick is going to be remote on/off of all or chosen lights from a fob.... It will be nice to have such a thing returning to the truck at night in the woods from hunting or some such...

Btw... I can't bring myself to buy rigid. They're overpriced by my reckoning... There aren't that many places in the world that make the diode, and most makers buy from Cree. Meaning, the casing, reflectors, and lenses may be better, but durn near all of them are using the same light source. And I'll spend a few dollars at radio shack to get a variable resistor, or even a three position variable resistor, before I pay rigid prices.

No, the voltage to your headlights doesn't change, the other beam is being used instead. It remains 12vdc or somewhere there about.

Most led will handle anything from 12vdc to 30vdc.. the more, the brighter but also you're cutting into the life. If you wanted to rig your existing led bar for dimming/bright, you'd have to introduce a capacitor (which stores and often jumps voltage) and a variable resistor.... Basically you'd charge to the capacitor/resistor with 12vdc and that would pass through to the lights... Call it standard brightness.. to increase the brightness you'd either spin the dial or throw a switch (fixed level) and jump the voltage to 24vdc.. poof.. brighter lights. Or... You could have 12vdc (current brightness) as your high setting, and just use a variable resistor to lower the voltage... The issue is that the led's will fire likely around 8 or maybe 9vdc, but be really dim... Which would be good for daylight running I reckon, but not much use otherwise. The low being the 12vdc brightness and high being likely triple the lumens at 24vdc (it isn't a linear scale, the output increases exponentially with more input) would be the most useful way to approach it.. for that you need either a capacitor or dual input 12vdc and an isoltated bridge for clean 24vdc.