How do you replace a power steering hose on an '86 mercury station wagon?

Go to your local auto parts store and buy the hose (or better yet both, the other one is probably ready to go since it's the same age). You will need to know year/make/model and engine size, and if you are buying only the broken one you'll need to know if it was the high or low presure hose that needs replacing.

The best tool for this job is a flare nut wrench. Use the new hoses to find the right size (or sizes) to fit the ends of the hoses, since hte car is an '86 it is about 90% certain it will use an SAE wrench, these are the ones sized in fractions (1/2" 3/4" etc.). Be aware there is a *small* chance the old hoses will be different sizes, but it is unlikely.

Also buy a can of PB Blaster, or other good rust penetrant, this will help loosen the nuts on the old hoses. A drain pan will be needed to catch leaking fluid, and you will need more power steering fluid (never reuse the old stuff even if it hasn't all leaked out).

Once you get home, open the hood and look for the old hoses, they will go from the pump on the front of the engine (where the belts are) to the steering box or rack (which it is depends on what mercury model you have). Once you find the hoses, compare it as best you can to the ones you bought to see if it looks like you have the right ones. If so it is a simple matter of spraying the nut on the end of the hose with the PB Blaster, loosening the nuts with the wrench. This can be hard if they've rusted in place, be careful that the wrench is the right size and on tight, then pull with all your might. Once you have the old one off, use the way it was installed as a guide to how to lay the new one, then *carefully* start the nuts on the end by hand, you want to make sure it is threading in straight or you'll strip the threads and need to replace some very expensive parts. Once you have them started by hand use the wrench to tighten them up. Check to make sure the hoses aren't rubbing up against anything that could damage them, then refill the system to the recommended mark (DO NOT OVERFILL THE P.S. SYSTEM). Start the car and turn the wheel back and forth a few times. Stop the car and check the fluid level and add more if needed. Start the car again and check the ends of the new hoses for leaks, have someone turn the wheel a little in each direction i you can to see if it leaks under load. If there are no leaks, you are done.