WHy do you need to know how to bypass everything in a furnace? Planning to burn a house down because you really left what you were trying to accomplish open to a lot of speculation? Because bypassing most things in a home heating system would create a very real and very dangerous fire and safety hazzard.

You don't bypass a limit switch, you test it to see if it is closed (or open) when it should be. Usually limit switches are closed until the temp gets above a certain limit and then they open until it drops below a certain temp. A 150-30 limit would open at 150 deg and reset at 120 deg. If it is still open when the furnace has cooled, it is faulty. This is just one possibility. There are waaaay to many to list them all here. You have to describe your problem and what you want to do better or you will not get much good help.

Right, you don't by pass a limit switch, it's there to protect you and they are resettable 99.9% of the time. Give us the brand and model of your furance and maybe we can help. Are you seeing any small flashing LED lights like maybe 3 flashes on a red light?