If your just dealing with the alarm/horn going off all the time, you can try disarming it when it goes off by putting the key in the ignition and turning it on and of three times ending with the last turn in the on position. This will stop the alarm from sounding.
If you have fuel coming out of the lines when you are cranking the engine then your fuel pump is working. You should only get a small burst of fuel when you first turn the key on and then nothing while the key is on, the ECU only tells the fuel pump to turn on when cranking and when it can see cam and crank sensor signals while the engine is running. The small burst of fuel you may or may not have experienced is only to prime the fuel rails. To test your injectors, you can buy what is called a "noid" light. They have them at most stores that have a good tool/automotive section, such as sears. You unplug one injector with the engine off, plug the noid light into the injector connector (harness side going to injector). Then start or crank the engine over and see if you can see the light pulse on and of very fast. You may need two people due to limited visibility while cranking the engine. Repeat this for the rest of the injectors. If you have an "ohm" meter, you can ohm check the injectors by disconnecting each one and touching the pins inside the connector cavity on each injector. The ohm reading should read between 5-20 ohms. I hope this info helps!
Seems as though you have a wiring problem if your injectors have no ground.
I suggest you check the wiring diagram to see how the injectors are grounded. If they are grounded by a common point on engine or chassis repairing or duplicating it should be straightforward but more complicated if both the injector pulse and the ground are provided by the ECU.
Start by removing the door panel then the switch.
The video below will show you how to remove the door panel and the switch.
The master switches on this generation of Legacy have been know to wear with age.
First inspect the mechanical movement of the window regulator behind the plastic water shield. This style of regulator uses a gear driven motor with scissor arms to lift the glass. Look for any damage to the gear or a possible jam. You might need small mirror and a flashlight to fully inspect the parts inside the door. The easiest electrical test is to jump the motor with a 12V power source and see if it runs. That should identify a faulty switch or motor.
If you need to replace the motor and or the regulator its a little more involved. I will gladly post that in another answer if necessary.
Lastly try the link below to locate a replacement switch if it is the source of the problem. Car Part com Used Auto Parts Markethttp://dgzmd7u6z2by7.cloudfront.net/partimage/WRG/1AWRG01938/large.JPG