• 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?

if it worked before and doesn't work now then at least one of these may be true;

• an electrical connection is compromised: wiring terminal loose, fuse blown / breaker tripped
• something was inadvertently turned off by physical switch or app setting
• something has failed or worn out¹⁾

if it it works sporadically then there is likely a loose connection or failing component. These can be tough to diagnose for reasons discussed in the next section.

If it's never worked then perhaps

• something is installed but not hooked up or turned on (see above)
• it wasn't installed
• it failed before you bought it and the seller didn't know or didn't say

It's also possible that it's working as designed but you don't know it. Example: “my charger isn't charging my lithium batteries even though they are not at 100%”.

When we can cause the problem at will we are very close to the goal line. We truly understand what is happening and all we need to do is figure out why. Sometimes we can google at this stage and get a direct answer: “firmware v4.3 has a bug where [yadda yadda yadda].”

Getting to this point can be time-consuming and frustrating. It's basically repetitive testing and observation until you can make the problem happen with the minimum of factors.

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).

Measuring voltage with a 'meter is fundamental to troubleshooting in a van. Let's assume a lava lamp plugged into your 120vac circuit no longer works. Anything between (and including) the battery and lava lamp could be causing the issue.

There are many points to test

1. the 12v battery bank voltage at the terminals
2. the 12v input terminals on the inverter
   1. the 120vac output terminals on the inverter
3. 120vac outlet where the lamp is plugged in (assuming it's not directly plugged into the inverter)

In practice we usually don't need to test them all. We can make some fair assumptions on our preliminary investigation:

• if voltage at the battery is low (lead) or ~zero (lithium) the battery needs to be charged. If voltage is normal the problem probably lies elsewhere.
• if other things are running off the inverter right now then the problem is unlikely to be the inverter itself. Note, however, that it's possible that the lava lamp pushes the inverter over its limits.
• if nothing is running off the inverter and there are not lights on it then a fuse may have popped. 0v at the inverter inputs will help confirm this.
• if the lava lamp doesn't run when connected to a normal shore power outlet at Starbucks then the problem is probably the lamp.

If things still don't make sense we might have to explicitly test those assumptions. Or test at each point.

• if the battery terminal voltage sags under load the battery is undersized and/or unhealthy
• if battery voltage is ok but low at the inverter terminals then the voltage sag is likely caused by resistance. Bad connections, undersized wiring, etc.

On wiring runs that do not have observable loads on them we might have to take a voltage reading at each one. If there are many connections you might start at the midpoint to rule out 50% of the possibilities, repeating until you find the offender or exhaust the possibilities.

Note: on circuits presently carrying power voltage testing is also indirectly continuity testing (see below). If there is voltage there must be continuity between the test points.

Sometimes voltage doesn't tell us what we need to know. Finding a parasitic load is often done by watching current going out of the battery and pulling fuses one at a time or otherwise breaking the subcircuits. When the offending circuit is taken offline the current will drop by that amount.

Current measurements are also important for understanding how your system is functioning: how much charge you're getting, etc.

If you have a battery monitor installed you can watch the net charge/discharge that way. Or you can use a clamp meter (see below). Or for small currents you can break the circuit and use the meter inline reveal the current. The clamp meter is the fastest, easiest way to measure current on a particular wire.

Meters can measure continuity. This might be useful for testing a fuse in the hand; it might look good but actually be popped.

Meters can also measure resistance but that is beyond the scope of this simple guide.

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.