fuse box on positive battery cable what is it for and do i need it to have my car started

My sisters brake pedal goes to the floor every now and then. From what I read it most likely seems that it has to be the master cylinder, please correct me if I'm wrong. There's no brake fluid leak and no air in the lines. If the Brake booster was bad it would make it hard to press the brakes, correct? Also, on this year car can you tell me what the brake bleeding order is(Ex. RR,LR,FL,FR)? Thanks in advance.

Can anyone provide me with the order that the brakes need to be bled? I'm changing the Master Cylinder this weekend on my sisters car and I want to make sure I'm bleeding them in the correct order. Also just to get another opionion on what's wrong. She said the pedal goes to the floor every now and then which I find odd that its only sometimes. She doesn't have a leak, no air in line so I would assume thats its a faulty master cylinder. If it was the brake booster it would only make it really hard to press the brakes correct? Thanks in advance for the help.

I know the struts are blown. I do not know if the springs are sagging. I have searched the internet for over an hour to no avail. Ride height is measured from the ground to the wheel well. Please advise.

My car is stuck in 3rd gear

The car turns over fine but just won't restart right away.It is getting spark so it is a fuel problem.The catalytic convertor clogged?It did catch on fire when the car was running rough.With a tune up it is running better.

He has also replaced the ignition switch and checked all the relays from battery to fuel pump. If we let the car sit for a few hours to a day, then it starts back up and is good for a week or two.

Trans jumped to reverse then back to drive going down road now no reverse only grinds

Now no reverse and grinds loudly

runs good when giving gas or in park only in drive

I checked the starter tested and it's good, what can I do?