People have asked me what my favorite tool is, and I have several answers to that, I have gone through several Swiss Army Knives, I'm always setting them down and leaving them somewhere. My favorite one had: philips driver, scissors, can opener, saw, file, punch, fish hook tool, ruler, etc.
Of course I love my little Leatherman tool, the file is the best I've
ever seen, the blade is a scalpel, and the pliers are very practicaland
strong, but, when push comes to shove, the one tool that saved me more
time, has fixed more cars, the tool that I carry in EVERY vehicle, the
unreplaceable tool, the one tool I'm frantic when I can't find, is...
Since electricity is invisible, (lightning bolts not withstanding) people are baffled by it. My test light gives me the ability to determine instantly whether electricity is present or not at a given point in an electrical circuit. When something electrical stops working, the first thing to check is if there is electricity getting to it.
A test light looks like a cross between a screwdriver and an icepick, with a small light bulb inside the handle and a wire and clip coming out of it somewhere. I have bought dozens of test lights over the years, paying anywhere from 99 cents to over 30 dollars for them. You should be able to pick up a quite adequate one for 5 bucks or so. If you want to diagnose any electrical problem on your car, it is the one indispensible tool.
Since it only has one moving part (The little clip at the end of the
wire), a test light is one of the simplest tools to operate that there
is. All you need to do is attach the clip to a good electrical ground
and it's ready to use. One of the nice things about automotive electrical
systems is the fact that"
Virtually all electrical components are grounded to the body or frame
of the car. That makes it simple to check for power. Two things go wrong
with the test light, sometimes the clip doesn't make a good electrical
connection, and sometimes the bulb burns out. To fix this, just wiggle
the clip a bit, or clean the metal off a bit. To test your test light,
just connect it across the terminals of your car's battery. It should
light up. Look at the images below, and you will see some of the various
styles of lights that are available.
Using the light to diagnose electrical problems is simple once you have an idea of how the circuit functions. One of the absolute best uses is testing fuses. I'm continually amazed how many "mechanics" still check fuses by pulling them out of the fuse block and looking at them. I wish I had a dollar for every time someone told me "I checked the fuse, it's good." I've seen a number of fuses that visually appeared perfect, but which were, in fact, bad. To test a fuse while it's in the fuse block, simply touch the exposed metal parts (ALL automotive fuses, no matter which style they are, have exposed metal on both sides of the actual fuse, for just this purpose.) with your light while the circuit is energized. If there is power at both points, the fuse is good. If your light only lights up on ONE of the contacts, the fuse is open. Simple. I can test every single fuse in the average automotive fuse panel in a matter of seconds.
The previous paragraph should be printed in all caps, in bright red type. It's probably the most important bit of information on this entire website. If you don't read any other information here, please read that one. Read it twice. If you don't own ANY tools, make the first one you buy (and learn how to use) a test light.
If you are serious about repairing your own car, basic electrical troubleshooting
is the most important skill you can acquire. The vast majority of car
repairs involve some amount of electrical trouble-shooting, and most people
(AND many mechanics) don't really understand how to do it. Buy a test
light, and then open the hood of your car, connect the light to the negative
post of the battery or to a nice clean bit of metal somewhere, and touch
the point to the positive post - the light should light up. Experiment
a bit, locate the starter solenoid or alternator, touch the point to some
of the exposed wiring connections. Locate the underhood fuse box, find
the exposed metal parts of the fuses and check them, note that many of
the fuses aren't hot at all unless the ignition is on. Play around, get
comfortable with the tool.