These tools are very useful and inexpensive. There are certainly differing brands and purchase methods as one desires. I will work on tutorials to help folks become productive with them.
Inexpensive Un-powered Test light, also called a Circuit Tester:
ATD Tools 5513 Heavy-Duty Circuit Tester or similar $10-15
This is a very useful tool for a quick check of power and ground on general circuits of a vehicle. It’s easy to use/visual but should never be used on electronic/computer circuits. You can go cheaper, such as the Harbor Freight model, but I prefer a bit more durability.
Harbor Freight CEN-TECH or similar: $5-25
This tool is barebones/cheaply made but does the job. The meter’s leads are the weak link, they tend to break near the connections if bent excessively. Price is right: $5ish, and FREE with a coupon if you time it right. I have one in every vehicle!
Sears Craftsman #82351 multimeter $40
This is a big step up from the CEN-TEC in sturdiness and useful features if Sears continues to sell it. Sears offers a lot of multimeters that look similar, shoot for this model # if possible. Here’s why: Frequency, Duty cycle, Relative, Data hold are helpful features that are typically found on much more expensive meters. The capacitance test is nice but not that useful for us.
Inexpensive code reader:
Autel MaxiScan MS-309 or similar: $25ish
This is a simple OBD-2 code reader. You’ll be able to retrieve and clear engine related diagnostic trouble codes when you see an illuminated check engine or service engine soon light. Some may also indicate system readiness status (OBD-2 system self checks are complete, you are eligible for an emissions test). Newer models contain code definitions and additional features. Does not indicate system data (sensor readings/other) or brakes/body/airbag/etc info.
Low/mid price OBD-2 Generic Scan Tool: $65-150
Autel Maxilink 529 or similar. $70ish
An OBD-2 scan tool goes beyond a code reader, displaying engine and some transmission data (sensor and other operating information) and freeze frame info, which is useful for diagnosis. OBD-2 Generic means you’ll see the legally required minimum of emissions related engine data, perhaps 25-50 PIDS (parameters), as opposed to the hundreds of multi system PIDS seen on a professional grade scan tool ($500-many thousands). Higher priced tools in this range ($125-150ish) display most transmission/SRS (airbag)/ABS (antilock brake) codes and perhaps oil life reset, EPB (electronic parking brake) reset, and others. If considering the higher end, look for a tool that displays data also in multiple systems (a maybe).