Those Pesky Ground Connections And Why They’re Important

“So, what was wrong with my car?” my friend Rick asked as I handed him his car key. “Glad you asked” I returned. “C’mon out in the shop and I’ll show you”. Rick had brought his car in, complaining about several strange troubles.

The engine would suddenly run rough and sometimes backfire. The “Check Engine” indicator flashed on and off at random. Warning buzzers sounded off at strange times. After I drove the car and verified some of these maladies and convinced my friend that his car probably wasn’t haunted, I pulled the car into the shop and onto the car hoist. Rick had business to do and left, saying he would check back the following day.

The first thing I did was to check for the presence of excess AC (or “Ripple”) voltage at the alternator output with an oscilloscope. I knew from training and previous experience that this could be the cause of many types of seemingly weird symptoms. But in this case, no such luck. The ’scope showed ripple content at less than 100 millivolts. I also verified this with a low-range AC voltmeter – same result. And the alternator looked to be nearly new.

Still thinking that this was an electrical problem, I began to test and inspect various wiring and connectors. All of them were clean and tight. Next was to suspect the ECM or Engine Control Module – the computer – itself. Its actually pretty rare for one of these to fail, but as with nearly anything electrical or mechanical, it does happen.

But again, no such luck this time. Substituting in a known-good ECM did not help. Same troubles. I was beginning to think that my friend Rick was right after all and that maybe his car was haunted!. I was thinking about contacting a local clergy to ask for advice when it suddenly hit me like a blast of loud music: Grounds.

You see, ground connections are very important in any electrical circuit – they provide the necessary return path for electricity to flow. If this path isn’t present, then the electrical current will do what nature and physics have told it to do – it will always seek the path of least resistance back to the source, thereby trying to complete the circuit on its own. The results are usually strange and unpredictable, especially if the ground connection is simply loose and not broken.

So back to Rick’s car. I began looking around under the hood once again. But nothing looked unusual nor out of place until I began to check closer around and underneath the alternator. As mentioned earlier, the alternator appeared to be near new, and I knew that Rick sometimes did simple car repairs himself to save money.

Then I spotted it! Yes! This was one of those glorious moments of revelation in which you not only know the answer, but you can actually feel it. When Rick had changed his alternator, he had neglected to reattach a small black wire which was normally fastened to a bolt at the lower rear of the alternator. This wire was also the primary ground for several circuits, including the ignition system.

I removed the alternator, reattached the black wire to the proper place, reinstalled the alternator, and all of my friend’s problems magically disappeared.

“I didn’t think it was important” Rick said when I showed him the culprit. “After all, its only a ground and there are lots more, right?”. Well, not exactly. Rick further explained that he had noticed the loose wire after replacing his alternator but didn’t want to go to the extra trouble of removing the unit again in order to refasten the wire.

Bet he won’t make that mistake again, and neither should you.