You are right, you might see a 1-2 MPH difference with the reduced electrical load on the alternator. But that small difference will be lost in the greater effects of variations in your driving habits. You could lose any gains from the electrical improvements in a couple of jack-rabbit starts at a stop light.

So you've dropped almost 30A load from alternator changing headlights? Considering most factory-stock alts. put out 80A, seems like you would increase mileage by a couple. Re-post when you find out.

Yes & No, yes it will increase the MPG if you dont use anything electrical but the amount of fuel you save is so small that you would have to drive about 5 years like that to maybe gain about 2MPG if your lucky. The costs of not having them on versus the money you might save is not worth the effort in trying to keep all electrical devices off. So I wouldnt even bother to be honest

You know those lights do not draw much amperage to begin with dont you???? The biggest load on the electrical system is the engine itself, the rest if minimal & not even enough to bother or be concerned with nor does the radio draw much juice as well. so your living in a cave like a troll to save maybe $.20 a year is pretty much what it amounts to

Also, you can cause weird electrical issues since the car knows there is suppose to be this set amount of voltage drop across "X" amount of bulbs but in changing them to LED's, the voltage drop will differ from what the car should see & can turn on warning lights or cause other weird electrical gremlins to appear

whe you consider that the alternator is only pulling 3-5 hp, the reduction most likely won't be noticed, but a pony saved is a pony to be used else where. as fasr as mileage, negligible.

I'm not sure

So I am switching ever light out in my car (except head lights) out for LED's. The lowest wattage ones... I have already done so. but they are super bright so its pretty good looking. (this includes dash interior read, license plates, tail lights, etc.

The headlights now have 55w HID's including fogs... each pulls 20 amps on initial startup but after doing my own tests I find them to pull about 3.7 amps each vs the constant 18 with each halogen bulb.

This is a huge electrical load decrease.

I mostly drive at night

Ford Focus SEL 2009 perfectly rebuilt. getting 41 mpg highway (55 mph) all the time before change but with the heady load. I havent actually gotten to drive much with the change.

I need a rough estimate on the amount that i will save on gas now that my alternator will not be running hard.. (i dont use the radios often and I have no accessories plugged in typically...

Im guessing 1-2 mpg. Maybe some of the smart autoheads can tip me off on whether this will increase the efficiency or no?

I did notice my engine RPMS do not lower at all when I initially turn on the lights unlike before. :D