Bad negative cable ground caused all kinds of weird problems on rainy days…
One of my cars is a 2007 Mazda6 with 130,000 miles. It's never had a problem until this spring. Twice we noticed that after extended rain, the car would suddenly do something weird. It was parked in the driveway (not running) and the horn started to blow. I disconnected the battery cables, cleaned them and the problem went away. A few days later, it was raining all day, the car is parked in the driveway and suddenly the emergency flashers on the left side of the car are flashing -and they won't turn off. This time, I did some net searching and discovered the harness to the body control module can develop loose pins. It's easy to get to so, all 5 looms were disconnected and cleaned with electrical cleaner/lubricant. Again the problem seemed to have gone away.
As fate should have it, we had no rain all summer and the car was just fine. Last week, it rained all day one day and bingo, the car was just sitting there and we noticed the right side headlight marker and right side taillight marker lights were on but the left side marker lights were not.
OK, this means war. Time to dig in and start checking grounds… Sure enough. Resistance readings from the end of the negative battery cable to various places on engine and frame are reading erratically (10 to 200 Ohms) despite solid connections to bare metal.
About 12" down from the negative terminal, the cable connects to a dedicated 10mm ground bolt on the strut housing and from there goes down to the starter. I removed the bolt and can see the connector is pressed against a clean painted surface of the strut housing. The threads of the bolt were covered with white surface corrosion. The ground from the connector was only being carried by the underside of the head of the bolt through the corrosion and into the strut housing. I cleaned the threads and also etched some of the paint away so the connector could make direct contact with the metal in the strut housing. There was one other ground strap to the engine so, that was checked and cleaned too. After this, the resistance is 0 Ohms between the end of the battery cable to anywhere on the frame or engine.
Well, it rained all day today. The car sat in the driveway -and didn't turn on any lights, or flashers or blow the horn, or act weird at all. I hope that's the last of that problem.
Ray
One of my cars is a 2007 Mazda6 with 130,000 miles. It's never had a problem until this spring. Twice we noticed that after extended rain, the car would suddenly do something weird. It was parked in the driveway (not running) and the horn started to blow. I disconnected the battery cables, cleaned them and the problem went away. A few days later, it was raining all day, the car is parked in the driveway and suddenly the emergency flashers on the left side of the car are flashing -and they won't turn off. This time, I did some net searching and discovered the harness to the body control module can develop loose pins. It's easy to get to so, all 5 looms were disconnected and cleaned with electrical cleaner/lubricant. Again the problem seemed to have gone away.
As fate should have it, we had no rain all summer and the car was just fine. Last week, it rained all day one day and bingo, the car was just sitting there and we noticed the right side headlight marker and right side taillight marker lights were on but the left side marker lights were not.
OK, this means war. Time to dig in and start checking grounds… Sure enough. Resistance readings from the end of the negative battery cable to various places on engine and frame are reading erratically (10 to 200 Ohms) despite solid connections to bare metal.
About 12" down from the negative terminal, the cable connects to a dedicated 10mm ground bolt on the strut housing and from there goes down to the starter. I removed the bolt and can see the connector is pressed against a clean painted surface of the strut housing. The threads of the bolt were covered with white surface corrosion. The ground from the connector was only being carried by the underside of the head of the bolt through the corrosion and into the strut housing. I cleaned the threads and also etched some of the paint away so the connector could make direct contact with the metal in the strut housing. There was one other ground strap to the engine so, that was checked and cleaned too. After this, the resistance is 0 Ohms between the end of the battery cable to anywhere on the frame or engine.
Well, it rained all day today. The car sat in the driveway -and didn't turn on any lights, or flashers or blow the horn, or act weird at all. I hope that's the last of that problem.
Ray
