I agree that bad connections can throw you a curve ball, but it's not THAT common, and the basics of checking connections and earth's is stuff you ought to do anyway as a process of elimination I think?
Power probe. Awesome bit of kit, and useful.... but also dangerous if you're not sure what the consequences are of applying voltage with one.
Plenty of people have blown expensive stuff up with a PP.... which doesn't happen with a MM.
I bought a Snap On EECT900 power probe a couple of years back and it's amazing. You can set the probe to momentary,latched or pulsed and you can even set a maximum current.Being a power probe is about 10% of what it can do. It's not cheap by any stretch but the time it saves makes a massive difference. My lad bought a Massey 3080 which has a couple electronic units which can cause issues. A previous owner had spent a huge amount of time bypassing all the systems, cutting into wire and basically making a dogs dinner of it all simply because they didn't understand simple diagnostic process. A few hours laying on my back with probe and someone in the cab we were able to prove all the systems were ok and reinstate all the wiringand the ECU. Most of the issues were simply down to bad connections which could have been fixed in a few minutes and some sticky hydraulic valves. Sadly it seems to be a pretty common story that people who don't understand things bypass stuff and proclaim they've made it better, very common in the Land Rover world.