Click here to go to the article about Halo 2 Overload Glitches.
The Halo 3 Overload Glitch can be done on Forge or in Multiplayer.
How to Overload Any Halo 3 Map
Overloading a map is usually done to disable the Guardians that prevent players from leaving the boundaries of a map;including the mines around Sandtrap and the turrets around Snowbound.
To overload a map in Halo 3, you must first start a Forge game. Go into edit mode by pressing up on the d-pad and spawn a trip mine. Open the spawn menu again, press X, and change the minimum run-time setting to the same number as the maximum run-time setting. Then leave edit mode, stand on the trip mine spawn and start dropping trip mines. You can drop trip mines faster by repeatedly pressing X and Y at the right speed. There doesn't seem to be a definite number of trip mines that you need, it depends on the map and the number of objects on the map, so a good rule is to just keep throwing trip mines until they explode on their own (usually 90 seconds after the first one is dropped). Once the pile has exploded by itself, the map should be overloaded.
After some experimentation, this can be done with other equipment. Spawn, say, a Deployable Cover and set it up like a Trip Mine. Then, press X and Y in unison multiple times, throwing for a good few minutes. Once you have thrown enough, the map overloads. This method takes longer than Trip Mines, however.
The Effects of Overloading
You will know the map has been overloaded because certain elements of the map will have been disabled. The Elephants on Sandtrap will disappear, the guardians on Sandtrap and Snowbound will become inactive for the rest of the round, shield doors will no longer function, and gravity lifts such as those on Construct will disappear or become inactive. Overloading a map may cause other glitches as well.
Once the map has been overloaded, you are free to walk outside the boundaries of maps such as Sandtrap and Snowbound, until you hit invisible walls. You can try to get past these walls by utilizing the Forge Turret Glitch or side seat glitch (requires two players).
Note: May cause the game to freeze on some occasions.
The Effects of Overloading
Avalanche - Unlike the other maps this requires you to overload the map multiple times. It's easy some times, but there is an easier way to. Go under or near the area of the Spartan Laser cave, then put the mines and overload the map like usual, and done, all mancannons are disabled.
Blackout - The air lift disables though the rushing air is still visible.
Construct - Gravity lifts no longer work.
Epitaph - The rocket launcher platform no longer functions and can be moved about.
Guardian - Main gravity lifts are disabled, hologram no longer works.
High Ground - Main gate disappears.
Isolation - Gravity lifts are visible but don't function.
Last Resort - Bridge which attackers use to get into the spinning wheel disappears.
Sandtrap - Minefield becomes inactive for the rest of the round.
Snowbound - Shield doors are cut and turrets no longer shoot.
The Pit - All major weapons (e.g Energy Sword) disappear temporarily.
Valhalla - Man Cannon is disabled.