What could cause a ground to go bad?

jmstrawn12

CarAudio.com Newbie
I recently upgraded my factory stereo with a new head unit, amp, speakers, and all the wiring and everything worked great for a month. Now the amplifier will work occasionally but most of the time will go into protect mode or not turn on at all. I checked all connections, ran resistance checks on the wires, and also did a voltage check on all power cables. I found that when the amp wasn't working there was between 6 and 7 volts running thru the system. When it does work is 12+ volts. I finally traced the problem to the ground cable which is connected to a long bolt that holds my passenger chair to the car. When I originally installed the ground cable I made sure to scrape away all the paint and use a brass battery lug to secure the ground wire. As mentioned it worked great for a month but now it isn't grounding properly. I removed the bolt and cleaned the area and the bolt with a wire brush then reassembled. It's still not grounding correctly. What could cause a previously good ground to go bad?

Mike Strawn
 
Vibration, moisture, corrosion to name a few. Was there anything wrong with the connection when you readdressed it? Factory ground points could be corroded.

Measure resistance between your amp and a known good ground. If that's good, and your cables are long enough, measure resistance between your amp and the negative battery terminal. You have to think of ground as a whole: everything between the amp and the battery post needs to be good. Any single weak point will cause a problem. That's why big3 is commonly recommended to circumvent any shortcomings with factory ground path.
 
Vibration, moisture, corrosion to name a few. Was there anything wrong with the connection when you readdressed it? Factory ground points could be corroded.

Measure resistance between your amp and a known good ground. If that's good, and your cables are long enough, measure resistance between your amp and the negative battery terminal. You have to think of ground as a whole: everything between the amp and the battery post needs to be good. Any single weak point will cause a problem. That's why big3 is commonly recommended to circumvent any shortcomings with factory ground path.
It's a brand new car bought a few months ago so no corrosion. The ground wire from bolt to amplifier was only 18 inches long so not a long run. I created a new ground wire and after connecting it I still had the same problem. I found another place to ground and it works just fine. For some reason this one ground spot worked great for awhile then all of a sudden did work as well.
 
This isn't a case of a good ground going bad. The ground was never good to begin with. Seat bolts make for bad grounds for a number of reasons - see link. My guess is you crammed the terminal between the bolt and the seat frame, which is a very common ground for amateur installers and prone to failure.

Hopefully you didn't just pick some other random bolt in the car for your new ground.

 
How did you attach the lug to the cable, and the cable to the vehicle?

My guess: Lug/Terminal jammed between seat bolt and seat frame. So the ground path would have been thru the treated washer to the treated bolt thru the threads of the bolt to the capture nut thru a couple spot welds, then finally arriving at the frame/body/ground.

Hope he didn't brush the paint off the seat frame, if so that needs to be repainted.
 
How did you attach the lug to the cable, and the cable to the vehicle?
I bought a large crimping tool that allowed me to attach the lug to the cable. I used a ferrule on the end of the cable that goes into the amp. I used ferrules and heat shrink on all the cables throughout the system. The seat frame has 4 bolts attaching it to the car so I removed one and ran the bolt thru the lug, thru the seat frame, and into the car frame. I did scrape off some of the paint on the seat rail to make sure it had a good metal to metal connection. With the seat pushed all the way back you can't see the missing paint. Plus I'll keep the car till it hits 500k miles then trade it in on a new one so I'm not worried about looks. My new ground spot is the large bolt that holds the seatbelt to the car. It's working great so far.
 
Seatbelt bolts - another notoriously bad ground spot for a lot of the same reasons seat bolts make poor grounds. Seat and seat belt bolts are great at anchoring a lot of weight, but weren't designed to conduct current. I assume there must be threads on here about how to select a good ground. Rear firewalls are usually good grounds. Anything that has a good 1/2 dozen or more spot welds connecting it to the floor pan is acceptable ground. The floor pan itself is a great ground. Most installers will drill and grind their own ground. Picking random bolts in the car usually doesn't work out.

Your seat frame is barely grounded.
 
"large crimping tool" hammer or hydraulic?

Seat bracket bolts aren't good. The seat brackets are usually completely painted and so are the floors. So many people tell you to remove the paint under the bolt, but to make a ground you would need to remove paint from on the seat bracket so it can ground through the floor, and remove paint off the floor where it would come in from the seat bracket.
MOST LIKELY if you didn't do that, you are currently grounding through the bolt, then through the threads, and possibly through the body to frame by bolt or by a grounding strap in the engine bay. Removing the paint you did, is most likely not helping in any way.

You really want to go directly to the chassis, or the thickest piece of metal you can that will connect to chassis. You can always make and add an extra ground if you are willing to find or make a hole on your frame, and connect it to where you are going. If you have a bolt that passes through the body, or you add a grommet and the wire through. (You really didn't say the size of your setup, if that's needed).

THE POINT IS: The seat bracket bolt is not good. You would be better off making a longer ground if you can get it to a better location.
 
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jmstrawn12

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