The real Jack McGinnis resides in a world of technical data, of analyzing data packets and, as an automotive service technician, must have great detective skills. When someone has an issue with their vehicle, you must be thorough in asking questions (can you spell C-o-l-u-m-b-o?). Questions like, "Did anyone work on it before?" Or, "Are there any add-on devices, like remote start, or a GPS, or an insurance tracking device?"
"Oh--and, one more thing, sir--how long has it been acting up?" A good investigator needs to jot down all the observations so as not to forget any important details.

I recently worked on a 2017 truck with a problem in the charging system. The alternator, battery, battery cables, starter and powertrain controller were all replaced. I checked the system for trouble codes--none. I did a visual inspection--nothing unusual. Look for clues, right? The engine computer said the battery was charging fine. A digital meter at the battery told be the computer was lying to me. Why does a computer lie? It doesn't. Garbage in = garbage out, right?

I asked a very important question: Was there any other work performed on the truck?

A: "Yeah--the radio was replaced."
Me: "A new radio replaced? Why?"
A: "Because it quit working one day."

I used my inspection camera and snaked it up under the dash, looking for more clues. I found an extra ground wire attached to the radio. The original ground was bad. The technician working on the truck probably replaced the radio and when it didn't worked, checked and found a bad ground. Rather than find where the ground was bad, the technician ran a separate ground. Now there were two grounds at different potentials. I cut the original ground and the battery started charging.

With enough electrical noise, the engine Body controller "told" the engine computer that the system was charging normally, so the engine computer backed off the charge rate.

It's all about detective work. What would have happened if I didn't ask about the other work performed? Probably an unsolvable case.