I don't own a HMMWV or an LED light bar, but perhaps my input on the Ibis Tek will be of help to you?
I did put a 66" Ibis Tek light bar on my M35A2.
http://www.steelsoldiers.com/showthread.php?125231-Ibis-Tek-Light-Bar-Install
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The Ibis Tek light bar has several flaws.
First, internally I found I had to disassemble the light bar and fix loose/bent brackets so that the ballasts did not continue to flop around damaging themselves and/or wiring. This was the case on every. Single. One. of the ballast in not only this 66" light bar, but all THREE of my other 24" light bars (currently not mounted).
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Second, in one of my three 24" Ibis Tek light bars, the internal electrical control module is completely exposed, it is not sealed in epoxy (like the other two) which means it is not weather safe.
Thirdly, the aluminum mounting brackets for the 66" bar are too weak. One of mine developed a crack in about 750 miles of pavement driving (with only ~30 miles on a maintained dirt road). I'm paying a very talented fabricator to fix and reinforce them.
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I still do like my 66" Ibis Tek light bar though. I enjoy the extra shade it provides my truck, I love the fold up cover to protect the lights for rocks/branches. So far, I would still recommend them, but only if obtainable for a
very good price knowing these flaws and if you are willing/able to fix them once received.