Here are a few things to check real quick. Ground strap from chasis to motor. Battery Ground, Battery Positive .Clean both of these very well and the terminal posts if cables corroded replace. Do a load test on the altenator if ok up to there then check the electrical coupler from alt. to wire harness this coupler gets very dirty from time to time and needs a good cleaning. If you still have original wiring this may need replacing also. If it is OK there and you still have a short then prepare to remove your dash and hunt the problem down there. I have found it is much easier to work on the electrical system inside the car after removing the dash just be careful not to damage anything as you pull it out. Most of electrical system will come out with the dash! Could just be a bad ground there. A good continuity tester is golden in these instances. Hope some of this helps it is exactly what I had to do. Good Luck!
The wiper motor on my GT shorted out some time ago and caused the same indications you are having (I think.) The fuse should have blown, but with my luck, it didn´t. One way to start the short isolation process without taking the dash apart right away is to pull fuses one at a time to see if the problem goes away. When the faulty system is taken out of the electrical system, by removing its fuse, the rest of the system should go back to "normal."
One piece of advice: Find a copy of the electrical system schematic for your vehicle before you do anything else. Take your copy to Kinko´s and get it blown up nice and BIG! On you new copy label and identify as much as you can when you take it apart. Maybe even invest in, or steal from you kids, a set of colored bencils or magic markers to colorize your schematic if it is in black and white. Don´t disconnect anything until you identify the circuit# and wire color on your schematic and know exactly where you are breaking the connection. This kind of attention to detail will pay off in spades in the end. If you can´t find a copy of the schematic at the library, try: http://clubs.hemmings.com/oana/tech.html
or drop me a line and I will e-mail or smail-mail you one.
PS The circuit designators that Opel uses, that is the # assigned to every circuit, is standard among the VW family of cars. That means if you are trying to hook up a fuse box, ignition seitch, relay of some sort, etc.., from say an Audi the circuit # that is assigned to that function will almost always be the same. Sometimes that helps with wiring things up.