I want to drive two XM-L's somewhere between 2A to 3A each (was expecting them to be in parallel with two separate drivers) for respectable output (meaning if someone sees my lawnmower coming their way in the dark they will "respect" me and get the heck out of my way! :) ).
-Garry
Maybe they will freeze like a deer with that amount of light. Fun to watch anyway. 
To drive 3 xml’s (in series) at 3 amps, you would need one of the following regulators with a .42 ohm resister connected to the center tab. Then the resistor and the left tab (your left looking at it) would to the + of your leds. The right tab would be connected to the + of your battery (or whatever). The - of your leds would connect to the battery.
The resister would need to be rated for a min of 3.75 watts. Use 5 2ohm resisters connected in parallel to get to .4ohms.
EDIT: If you use 5 1watt rated resisters, that would give you 5watt capacity. The watts are so low because only 1.25 volts is being applied across it.
EDIT2: You could have a switch to cut out 3 of the 5 resistors. When the switch is off, you would be driving the xml’s as 1.25 amps. Which would still be about as bright as a TR-3T6 on high.
Ok, take me like a hour to find this, I hope that this make all the job…
It’s constant voltage out, not constant current. And at 9-12V out can only do 1 amp…
You cant adjust the output to 3.7volts and connect the Leds in parallel?
I just check that your mower is 12v DC.
To which vehicle you want to place the LEDs?
To the mower you dont need a rectifier. I dont know the other…
I’d definitely run wire from the battery.
1. you can leave the stock wiring unaltered, so that you can revert to stock. that way, even if the thing is ragged when you sell it, you can recover your leds and driver w/o rendering the tractor useless except daytime.
2. i’m an electronics dummy…and won’t want to figure out how to make any other solution work 
Also, I’d probably consider xml ezwht - since I know there are 12V/1A LED drivers - I forget their max current, but I’m sure you could do 2 x 6V in series with one driver, and probably get away with 2 x 12V with 2 drivers if you use sinkpads and good heatsink
I verified my mower is 18v to 18.25v AC. I want to put the LEDs on the mower, not my snowblower.
Thanks for your links. Was almost ideal. I can't believe this is so hard!
-Garry
Take one of these:
http://www.ebay.com/itm/DC-4-5-30V-to-0-8-30V-Buck-Converter-Constant-Current-Battery-Charger-LED-Driver-/130898326824?pt=LH_DefaultDomain_0&hash=item1e7a25f528
Connect AC from the mower to a bridge rectifier with a filter cap (say 2200 uF) on the output and feed that to the driver. Drive 3 XML’s in series… maybe 4…
That does sound like a nice option. Not sure how I'd mount it. Guess I can use it to drive two XM-L's in series? And with this would I even need to use my drivers? Would using the drivers add a layer of protection? Connect both drivers in parallel from its output?
-Garry
It should drive 2 XML’s just fine. And yes, it would replace your drivers.
The mower had starter? How do you start it? If has starter have battery, if have battery already have rectifier.
Any ideas of this AC/DC to DC voltage regulator I found? It's rated 2.2A max (varies based on input/output voltage apparently), but I don't know what the max output would be with 18v AC input and +/-5v output. I really like that it incorporates a bridge rectifier onboard. I don't like the big potentiometer that could get knocked after I set the output voltage to what I want.
This module would also let me use the existing 18v AC wiring at the existing headlight connector.
-Garry
It’s a linear voltage regulator. Will get freaky hot and probably die a horrible death…
Out of curiosity. If you ever get a chance and feel so inclined, please measure the voltage at your battery while the motor is running (say mid throttle). That may be hard to do though if you have the battery under the seat and a seat safety switch.
That's not a problem at all; the safety switch (i.e. "dummy switch") has been disabled. I actually didn't do it on purpose; the wires fell off and I just left it that way! Not sure when I can get around to doing this though.
-Garry
What is wrong with this one?
http://item.mobileweb.ebay.com/viewitem?itemId=370802793797
Already had too the bridge, you can adjust the voltaje to 7.2volts and drive both leds in serie.
The poor lm2596 will very likely die an unpleasent death on that PCB if one actually pushes 3A trough there.
One could desolder it and mount it on a proper heatsink tho.