You read it over and over on Vortex...my Corrado won't start/dies randomly!...is it a bad ECU/ignition swtich?...on and on it goes.
In an automotive electrical system, DC flows from the Alternator and battery (+) Positive through the component then back to the battery (-) Negative. In between is all the wiring, switches, and relays that control the components. The big thick wires always carry the most current flow - they have the biggest loads.
First and foremost, you must remember that an electrical system is only as good as its connections. If you have shoddy grounds and sketchy wiring there IS going to be trouble. The car will operate poorly or not at all if the ECU and other components are not getting the proper voltages. The key to getting the proper voltages is to have good grounds, followed closely by nice tight connections at all the terminals.
Step one is to make sure ALL grounding points are in good shape. You can probably solve a majority of your issues by doing this.
Start at the NEGATIVE (-) terminal post on the battery. Clean both the battery post and the clamp on the cable. Make sure the clamp is securely fastened to the cable and then clamp it to the post. (Hint: Unless you have an Optima, use those little felt rings on the battery posts to help prevent corrosion.) Work your way back to all the grounding points and give them each a good cleaning with a small wire brush or a Scotch Brite pad after removing the terminals, even an emery board will do. Corrosion and dirt at these junctions increases resistance causing heat and preventing correct voltage drops. The components will not function properly if the voltage is not correct. This is especially true at the starter. Many times the starter solenoid will not engage or the starter will not turn over if their grounds are compromised. Check each grounding terminal in turn by removing and cleaning the contact points. Make the metal as shiny as possible. Give a firm tug on the terminals and if any of the lugs are loose, it's time to replace them with new crimp-on's (or solder up new ones if you have the skills). A good crimper is on of the most valuable tools in your box. Get one with a box of the popular sized terminals/connectors and a roll or two of vinyl electrical tape.
Step two, once all your grounds are clean and tight get to work on your fuse and relay panel. The wiring here is a bit harder to access and it looks confusing because it is all jammed together in a tight space. Most of the time your troubles will be caused by a connection that has come loose from the back of the fuse and relay panel. The thing to remember here is that there is a locking tab that allows a technician to unplug wire looms from the back of the fuse/relay panel. Make sure the tab is in place to keep the looms from coming loose when you kick the panel with your size 11's.
Fuses blow because the circuit they are on is overloaded. That means there is a problem with that circuit. If you put in a bigger fuse than specified, you are risking a fire in your wiring and possibly burning up your car! Usually a fuse blows because there is a short in the circuit. That is the positive side of the circuit (before the component) is making contact with the negative (ground) side (chassis, engine block). Shorts are the result of insulation that is breached or broken somewhere allowing battery voltage/current to go directly to ground.
Also keep in mind that relays go bad from time to time. Relays are just little remotely operated switches that use a low current/voltage to control a higher current load. Relays are cheap and easy to replace. But they are harder to identify by sight when they do go bad. Most non-start/random die offs are from the Digifant Control Unit Relay (in position #3). It powers up the ECU and if it goes bad the ECU will not function. Cut wires and broken insulation are other common issues.
Another common problem is the ignition switch. It is relatively easy to replace. Once the little screw is removed it is plug and play. I've done this a couple of times. On my Corrado, I had trouble with the wiring right near the plug that goes to the ignition switch. It actually burnt up to the plug. The wiring gets hacked up from PO's stereo and alarm installs. Again, the best thing you can do is make sure that the connections are in good shape and fix them if they are not.