Im having trouble with many things such as fog lights, headlights, headlight motors, and the horn. But can I use that thing under my dash and will it dish out electrical codes? If not, what type of testing do I have to do to figure out whats wrong with my wiring to all of the components Ive listed?

 

First, if it all possible get your hands on a wiring diagram.

The first thing I noticed from your post is that all of your problems seem to come from front end lighting. All of this is probably on a common harness. See is there are any obvious signs of problems with that wiring harness. Look for attempted repairs or someone splicing into the harness. But the easiest way to diagnose the problem is with a wiring diagram. Write down everything that is not working. Start tracing each item back to the alternator, you will likely find that everything having a problem travels through a common fusable link, horn relay, wiring harness connector, or some other common point. This will point you to the problem area.

Steve