Your local parts store provider could answer that question and also give you a price.
Failed brake line.
Length of back brake line to replace. hole in it between front and back door
In most cases the front section of the master cylinder Rear brake lines are "T'd" at the center of the rear axle
The proportioning valve is on the drivers side in the rear, just follow the brake line from the wheel cylinder, rubber line, you will see it at the end of this line.
You can cutoff the rear brake line. You will no longer have rear brakes and the fluid will leak out. It is not recommended that can't off the rear brake line, without replacing it.
The brake line will have a retaining nut on each end of the line. Loosen the retaining nuts. Reverse the process to install the new brake line.
Your brake line should run inside the drivers side frame rail ("C" shaped), angles up at the gas tank and over the rear axle. It splits and runs another line along the rear axle to the passenger's side.
the valve on the rear brake line is to limit brake force on the rear ie.loaded full pressure,empty reduced pressure to stop the rear brakes locking.
The lower line that is toward the front of the car.
Did you mean how to check your brake fluid? If you open the hood of the van, on the drivers side up near the firewall there will be your booster and master cylinder. On top of that is your reservoir . There should be indicator lines telling you if its full or if it should be added to. As far as checking the fluid in the lines, the only way is to bleed your brakes. Always start with the brake that is farthest from the master cylender with is usually the pass. rear brake then work to the drivers side rear, then pass front the drivers side brake..
Air in the brake lines. Severly worn break pads. Worn brake boost piston. Cracked brake line on that brake. Loose brake line.
rear car lights come on as an indication to the drivers in the back that you are about to stop.