Electrical diagnosis requires a good listener

Electronics Diagnosis

Recently we had a new customer drop of his Overland Park Acura with an electrical issue. Intermittently, the radio lights would go out and the radio/interior light fuse would blow. It did not seem to be related to driving over bumps or turning anything on or off. The customer would replace the fuse, go to work in the morning and find by the time he got home after dark, the lights were out. He had purchased a package of fuses and kept replacing them until it became too much of a hassle.

Initially he took the car to another Kansas City auto shop where they found some frayed wires in the driver’s door jamb. The wires were repaired, but the problem persisted. Thinking it may be the radio, he took his car to a stereo shop where they completely disconnected the radio again to no avail. The stereo shop, which we do a bit of business with, referred him to us. I really enjoy tackling these types of electrical issues. They are sometimes a challenge, but if we follow our step-by-step process we find the source of most all of them. Of course the vehicle has to cooperate as well.

A fuse is used for protection and cars are full of them. They basically keep things from getting worse and costing more to repair. Let’s use a simple cooling fan motor as an example. An electric fan motor requires a certain level of voltage and a certain amount of amperage to make it work. If the electric motor is faulty and “pulling” too many amps, the protective fuse will blow, which keeps other important wires from melting. Obviously, the device will not work if the fuse is blown.

Electronics Diagnosis

In the case of the Acura, we took the factory wiring diagram and looked at what devices were downstream from the fuse. We installed a temporary circuit breaker which resets itself in place of the fuse. The blowing fuse in question powered the radio light, the interior lights and the trunk light amongst other things. We started out by simply turning on and off all the lights in question to see if the breaker would trip. The breaker finally tripped when we moved the driver’s sun visor which housed a lighted vanity mirror. Next we removed the sun visor enough to unplug the electrical connector, but the problem was still there. Following the path of electricity “upstream” we got the problem to act up again by lightly tapping on the headliner. Further investigation revealed the power wire was routed incorrectly from the factory and gently rubbed through the insulation on part of the metal roof bracing, finally creating a “short to ground” causing the fuse to blow (photo 1).

We repaired the wire by adding a longer new section and re-routing away from anything sharp and reinstalled the visor (photo 2). No more blowing fuse!

If you ever find yourself in this situation, it is always very helpful to take notice of what was happening when a problem occurs. In this case the customer would subconsciously lower the sun visor on the way home from work, pop the fuse, then notice the lights were out when it got dark. Our Overland Park auto technicians do listen to all the details and in this case he acted on a good hunch, by putting himself in the customer’s shoes.

Photo 1: We found the power wire was routed incorrectly from the factory and gently rubbed through the insulation on part of the metal roof bracing, finally creating a “short to ground” causing the fuse to blow.

Photo 2: We repaired the wire by adding a longer new section and re-routing away from anything sharp and reinstalled the visor.