Troubleshooting my low-beam relay was very enlightening

Excellent article and story-telling. My electrical story of woe may seem to contradict your assertion about wiring diagrams, but it really just shows that, in some instances, it may actually be a great benefit.
My 1969 Porsche 912 had no official “factory” wiring diagram, so when the turn signal switch stopped working recently and I had no luck diagnosing it, my 912 Registry members assisted me in finding a corrected diagram produced by a fellow member. Even with that I could not diagnose why the turn signal switch did not work, so I then sent it off to a switch expert.
He and I communicated via emails and consulting the diagram. He pointed out that the turn signal switch circuit had multiple dependent relays in it due to the multipurpose signal switch stalk.
Using that diagram and usage data from me, he determined that the emergency light flasher switch, which was in the turn signal switch circuit and disabled the turn signals when it was “on,” was either defective or not fully disengaged, thus keeping the turn signal switch “disabled.”
I then sent him the e-switch, which he fixed. Now both devices work as they should. In this instance, the diagram was invaluable.

Reminds me of my time in Univ. AutoTech in the mid 70’s and the instructors advising if you go to turn your right side blinkers on and instead the left begin to flash dimly, chances are you’ve got a bad ground in your system. Can you imagine trying to trace all that using wiring diagrams? Best scenario is to use all your tools at hand and begin with electro/mechanical devices as the author states. They’re the weakest link, unless it was produced in the 2000’s in the age of computers where a computer will typically be needed to identify the issue.

As a side note, had a cute girl in college ask me to help her on an intermittent problem with her Gremlin shutting down going over bumps. Traced it to her coil. But while under the hood noticed AMC went cheap and the right turn signal and washer pump used the same connectors and were side by side. A quick switcheroo and two days later I got a follow-up call to find out why every time she turned right her washer would go squirt-squirt-squirt! Callbacks as it turns out aren’t all bad!

I appreciate your love of relays and the standardized terminal layout. But I love wiring diagrams. I can look at the diagram and know how the circuit is supposed to work. The diagram certainly tells me more than the manufacturers diagnostic procedure does.

Excellent primer on Troubleshooting 101!! Being able to properly Troubleshoot and being disciplined enough not to skip a step will work every time. The wiring diagram will simply show you were your troubleshooting test points are located in a circuit. Pick one end of the circuit and work your way to the other testing and proving “known good” until you hit a suspected “unknown bad”. To prove the suspicion either exchange the “unknown bad” with a “known good”, or go to the other end of the circuit and work back the suspected “unknown bad”. Once isolated and now proven “known bad”, either replace or repair the issue. Sounds simple enough; but I cannot tell you how many times I have seen proper experts get ahead of themselves with a hunch and end up chasing their own tails. Basic troubleshooting; learn it, know it, live it! It a practical tool with pretty much use in everything in life!

I agree; I’m so happy I have the wiring diagrams for my rig. Saves me lots of headaches troubleshooting. Of course I think it makes a big difference when you’re the original owner and know the wiring hasn’t been hacked to death (or at least you remember the hacking you did).

As for relays, you can learn from the experience of fellow enthusiasts of your vehicle where the trouble spots are. For example, the headlamp current on mine passes directly through the steering column switch, and these often fail after years of use. They’re not cheap or necessarily easy to find. So use relays to reduce the amount of current the relay has to carry.

Re: Italian wiring: I was once told by a Fiat dealer (circa 1980 something) that the “wiring diagram” on a Fiat depended on which factory workers did the wiring on your particular car, as they all had differing opinions as to the right way to do it. Separately, I bought a brand new Fiat 850 Spyder in 1970 and within a year the brake failure warning light was permanently lit and the headlight fuse burned out every time you turned the heater on. Also had some other electrical problems that I can’t recall.

My Mini is positive ground. Would this effect anything other than the terminals on the battery?

@david4 - Nothing significant would change. It is still the same two connections for most connections, just need to be more cognizant of wire color if you are familiar with one and are then working on the other.