No shortcuts to diagnosing shorts

No radio makes for tough day at the beach – logically.

I have a dear friend named Kurt that I have known for many years. Kurt is a mechanical engineer like me and we have spent much time discussing at length the whys and what-fors of most anything mechanical or electrical. How do you think this works? Why did someone design this so poorly? How much does this weigh? I love to engage in these logic-centered conversations and he is the perfect friend to share them with.

Anyhow, Kurt’s wife and three young boys were planning a trip to the South Carolina beach near their home on Sunday and the radio quit working in the minivan Saturday morning. Kurt called me around noon Saturday to discuss the scenario. He found the radio fuse under the dash was blown. With a few simple tools, he logically disconnected the radio, replaced the fuse, but it blew again when he switched on the key. He called when I was sitting at my Overland Park shop with access to the factory wiring diagram. I found the “radio” fuse also supplied power to many other areas of the car, like the security system, the auto door locks, the dome lights, the vanity mirror light, the seat belt warning light, and so forth.

If you have ever taken a wire coat hanger and bent the wire back and forth in the same spot, you know it eventually breaks. Growing up in a rural area, this is what we did when we had no pliers on hand to cut wire. If you think about it logically, car wiring is the same. If the wire that feeds your electric window motor gets flexed enough times by opening and closing the door, the wire will eventually break. And, it’s always the driver’s door that goes first – logically.

I asked Kurt if he had any problems with the other circuits I mentioned over the phone. He said, “No, not me, but my wife has a real problem with the passenger side vanity mirror!” The passenger sun visor has a lighted mirror under a plastic cover that appears once you lower the visor. A tiny switch in the little cover turns the light on when you flip it up. Apparently, the sun visor never stayed put, always dropping down on its own, therefore constantly flexing the wiring back and forth. Logic again tells you the wire will eventually break – which it did.

Kurt unscrewed the visor from the roof and unplugged the electrical connector, replaced the fuse and then, voila, the radio came on. In this case the power wire rubbed through to the ground wire making a clear short to ground which blew the fuse. In most cases, a wire will just come apart and not short to ground, which actually makes it more difficult to find. At New Concept Auto Service we use a different set of tools to find these types of circuit problems.

So, after lots of time invested in diagnosis, mom and the kids made it to the beach the next day. The kids listened to their favorite music and, most importantly, mom was happy and able to relax more.

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