LED's on my M998

I originally posted this under the wrong heading so:

For the short time I have been part of this forum, I have read MOST EVERYONE'S knowledgeable input on numerous topics so I am going to hopefully going to be able to pick everyone's brain on this one.


My wife bought me new LED headlights for my 1986 M998. They, according to the seller, were compatible with a Humvee installation.

My current stock headlights (original military issue) work fine as expected, My issue is that when I installed the led headlights (three prong installation) my low beam work fine, at +24 volts on the meter, however when I hit the high beam switch, not only do my high beams NOT come on but the low beams go out as well. In this particular application at high beam settings, both lower and high should be on simultaneously.....When putting the meter on the high beam setting, my meter shows a Negative 24volt read out????? , I replaced the stock lights and everything works fine....Where am I going wrong or what can I do to fix this issue. I am a jack of all trades here but my 24 volt understanding is limited....Thank you for any guidance you may have to share on this subject.

Rich (Richdane)

Sounds like they're not hooked up properly, meaning you've got one or two wires flipped. There are only 3 wires going to the headlights, but they're labeled, so it's not hard to check them. The TM here shows the wiring, though it will take a little tracing to figure out which is High and which is Low.
https://www.steelsoldiers.com/showthread.php?165063-Tm-9-2320-280-3-Maint-Manual-M998-Hmmwv-part-3
That said, they are labeled inside the housing too, so you can verify you've got the three wires into the back of the grill connected to the same numbers inside the housing.
At that point, you have only two wires to worry about, High and Low, since 91C is ground.

Standard 3 prong connectors follow this pattern for the beams and ground: looking at the plug, prongs facing you with the center prong up: right is ground, left is Low and top is High. Reverse Low and Ground if you're hooking to a female connector, since looking straight at it is the mirror image of the male prong connector.

Hope this helps.

Bulldogger

Although I was very careful in doing just that, matching wire for wire, Your suggestion has sparked another possibility, which is that when I had the lights apart for cleaning and painting several months ago, I may have plugged in the wrong leads in the inside of the Hood when reconnecting them....thanks for the information, I will have to pull this all apart before the cold weather really sets in AND before I go crazy running this wiring schematic through my head a million times....either way, thanks again !!!!

they could be bad units. Last few years they have been releasing LED headlights that did not have low beam, but Hi beam. I bought a pair because I don't use low beam anyways. Getting to my point. After 20 miles of washboard dirt roads, my low beam magically work now. If your wiring is right, the units are bad.