The root cause of most electrical problems is poor connections. Most problems are fairly easy to locate trough the process of elimination. A good quality DVM (digital volt meter) is an invaluable tool. Don't use a test light to probe circuits or serious damage could result.

Grounds: The ground path for any electrical device must be as good if not better than the power connection to it. When troubleshooting an alternator whine in a radio or even a quirky problem with the on board computer it is most often a poor ground. It is very common to see ground straps between the engine and body or frame disconnected or cut. These straps were put in place for a purpose. If the manufacturer didn't think they were needed they wouldn't have wasted the money to put it there in the first place. When troubleshooting an electrical problem always check the grounds. Many components rely on the body or chassis for their ground. As a vehicle vibrates down the road these connections can rapidly deteriorate. When checking a body panel or frame location for a good ground always use an Ohmmeter between the suspect location and the - battery post or other known good ground source. In many cases a Voltmeter placed between the + battery post and the suspect location will still show 12V. This is due to the almost non-existent current draw of a Voltmeter.

Splices: Crimp connectors are great little things. It makes an electrical repair quick and easy, but they are not for the automotive environment. Crimp connections have a tendency to allow moisture to get inside them and corrode. A properly soldered and weatherproofed connection will last indefinitely. I personally prefer to use heat shrink tubing as opposed to electrical tape to insulate the connection, but if properly done tape can do a good job. Remember the splice should be as good as the rest of the wire and a connection that is held together by pressure alone won't last. Crimp connectors work very well when soldered on.

Fuses: We have all seen it and some of us have done it, but DO NOT USE aluminum foil in place of or in addition to a fuse. Fuses do on occasion blow, no big deal, just replace it. If the fuse blows again when you replace it it's time to find the problem. I have never seen an electrical problem fixed by replacing a 5 amp fuse with a 30 amp fuse, but it's done all too often. The wire coming out of the fuse box is gauged for the current that circuit is intended to carry. If you need to add a device with substantial current requirements (like an amplifier or fog lights) you need to run a new wire of the proper gauge with a fuse at the battery.

Factory Harness Connections: Sometimes simply disconnecting and re-connecting some components will fix a problem. The connectors (especially those under the hood) are exposed to heat, moisture, and all the other stuff that comes off the engine and road. Be very careful when disconnecting these, many of the connectors will get brittle with time and can easily break. You may notice a white or clear substance in side the connector. This substance is known as dielectric grease, it's purpose is to keep moisture out of the connections so don't try to flush it out.