• troubleshooting is more about methodical thinking than specific techniques, tools, or tricks
• a multimeter is extremely useful and does not have to be expensive
• carrying a few inexpensive replacement parts and tools can be helpful when attempting field repairs

There are at least two different kinds of normal. Both are important to understanding how your system is misbehaving.

• normal according to the specs - the DC-DC charger is rated at 40A
• normal for your setup - maybe you see 37A-38A in Bulk while driving down the highway, and 25A at a stoplight.

After you get plenty of “seat time” in your rig you will know what is normal for your setup. Until then you really only have the specs for comparison.

Knowing what you have is important. It helps you understand what should be happening, and helps you communicate any problems to folks who might be able to help.

If you built your own system you know what is where and why (you put it there!). If you bought an all-in-one the manual will say what you have. Figuring out a prebuilt van may be the hardest of all since you might not have all the information, or parts might be hidden from view, etc.

The hardware is the physical stuff: components, wires, fuses, lights, fans. Look for brand and model info on everything and store the list somewhere for future reference.

This includes apps (name, OS, and version), firmware (version), and any settings or profiles that exist.

There is a famous saying that

clearly stating the problem is 90% of the solution

Sometimes just asking the question aloud or writing it down triggers something in our understanding of the situation.

It can help reveal faulty assumptions about how things work or whether or not they are working right now. A “second pair of eyes” is also helpful in spotting faulty assumptions. Get used to asking yourself questions like

• how do I know that?
• is that really true?
• did I actually test it?

We've come this far in the process and this is our first attempt at doing what most people think of as troubleshooting (testing with a multimeter).

Multimeters are called such because they can make multiple measurements. For our purposes we will use them most often to measure voltage at different points of the system.

For general purpose use even cheap meters will work. Advanced users seem to prefer prosumer brands like Fluke, but those users probably aren't reading this page. [YT video: iFixIt Basic Skills - Multimeter]

Note: if you are buying a new meter it can be useful to select one with a clamp to measure current. Read the descriptions carefully; DC current measurements are usually more useful for 'dwellers, but some models can only measure AC current with the clamp. Having both abilities would be preferable. [I bought this one - secessus] [YT video: Clamp Meter Automotive Measurements]

• YT video: Simple Troubleshooting on Board - Ask The Expert with Nigel Calder. Nigel is from boatworld but his knowledge is transferable.