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Weird Electrical Problems Due To Bad Ground. #5245409 10/20/19 07:59 PM
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RayCJ Offline OP
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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

Re: Weird Electrical Problems Due To Bad Ground. [Re: RayCJ] #5245421 10/20/19 08:18 PM
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mattd Online Content
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Ground connections are more critical than people think IMO. This is a common occurrence.


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Re: Weird Electrical Problems Due To Bad Ground. [Re: RayCJ] #5245427 10/20/19 08:21 PM
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Donald Online Content
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And then there are all the weird things that can happen when trailer lights have a bad ground.


2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
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Re: Weird Electrical Problems Due To Bad Ground. [Re: RayCJ] #5245496 10/20/19 10:08 PM
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There is a powerstrokehelp video on youtube that showed how a bad ground can also kill a transmission.


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Re: Weird Electrical Problems Due To Bad Ground. [Re: mattd] #5245537 10/21/19 01:06 AM
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Originally Posted by mattd
Ground connections are more critical than people think IMO. This is a common occurrence.


So true.

I'll never forget the Chevy service manager, while I was in his shop chasing an electrical gremlin, tell me:

"The black cable doesn't matter since it doesn't carry any electricity" Called it black, not ground.

I never went back there again.

Several years later when GM had their bailout and dumped about 25% of their dealers, that dealer was on the chopping block.

Last edited by user52165; 10/21/19 01:20 AM.
Re: Weird Electrical Problems Due To Bad Ground. [Re: RayCJ] #5245632 10/21/19 06:03 AM
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RayCJ Offline OP
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FWIW: It was humid and drizzling all night and the car seems to be fine this AM. It's parked in the driveway, the battery is not depleted and the security cameras only got triggered by a couple raccoons.

I don't find myself doing much automotive electrical work and this problem took me by surprise. The car has performed flawlessly over the past 12 years. It took me a while to realize that the BCM (body control module) is a computer with independent relay control over most non-engine-related electrical circuits in the vehicle. Also, the BCM controls the alarm system and wireless doorkeys and thus, is always operating.

Makes perfect sense now... If a small micro-computer does not have a clean ground, it will freak-out in strange ways. I guess I'm lucky the windows didn't roll down in the middle of a rainstorm!

Ray

Re: Weird Electrical Problems Due To Bad Ground. [Re: RayCJ] #5245644 10/21/19 06:19 AM
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edwardh1 Online Happy
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Toyota seems to have done good grounding.

You can always for some cars get some stranded 10 gage wire from hardware store, solder on lugs, and connect engine block to the chassis under any nearby bolt. I did that on a maxima.
Having a garage may help some too. wonder if there have ever been studies of electrical problems on cars garaged versus cars parked outside

Last edited by edwardh1; 10/21/19 06:23 AM.

These products are all new every year?? They are a revolution!!! Razor blades, mens shirts, TVs, wiper blades, gutter guards, hearing aids... according to the ads. But also all new last year
Re: Weird Electrical Problems Due To Bad Ground. [Re: RayCJ] #5245717 10/21/19 07:55 AM
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I have fixed a LOT of very weird, puzzling vehicle gremlins by just running extra ground jumpers here-and-there until the problem went away.


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Re: Weird Electrical Problems Due To Bad Ground. [Re: edwardh1] #5245727 10/21/19 08:06 AM
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I don't know about the inside vs outside, but take a gander at the SouthMainAuto YouTube channel and see what electrical gremlins show up in Upstate NY when cars are exposed to road salt and the occasional critter that eats wire insulation.

Originally Posted by edwardh1
Toyota seems to have done good grounding.

You can always for some cars get some stranded 10 gage wire from hardware store, solder on lugs, and connect engine block to the chassis under any nearby bolt. I did that on a maxima.
Having a garage may help some too. wonder if there have ever been studies of electrical problems on cars garaged versus cars parked outside


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