A lot of questions get asked about what to do in situations when i4wd does not work well, typically this will be very technical rock crawling and mudding. There are some known issues especially with mudding where the machine seems to bog down, or the front axle is automatically disengaged by i4wd due to excessive binding.
Most common "fix" is the bypass harness. It "bypasses" the ECU to manually supply 12v to the front drive clutch so that the i4wd system and ECU still think you are in 2wd. This is usually effective for mudding because it mostly disables Torque Management (the cause of "bogging"), and disables brake traction control (some loss of forward momentum), while leaving the front diff's default torque biasing in place. This is NOT a solution for very technical rock crawling, and when you hear the term "lock" used with it, it is "locking" the front axle engagement clutch on, not locking the front wheels together.
TorqueMasters has recently started selling a ratchet style locker that replaces the mechanical torque biasing components of the front diff. This can be used in conjunction with a fully stock ECU, a bypass harness, or tunes. It fully locks the front wheels at all times but can "ratchet" internally to allow easy turning. This works great for highly technical rock crawling, but keep in mind that it does increase stress on other components of the drivetrain. It does not necessarily solve the bogging issue, a bypass harness may still be required.