Author Topic: How do you find a bad ground?  (Read 3241 times)

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Offline ChopSticks

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How do you find a bad ground?
« on: June 07, 2015, 01:44:02 PM »
Alright so my 2009 Sportster (Nightster) has two grounds, a engine chassis ground which is the cable from the negative battery terminal to the engine, and a powertrain ground which is where all the components (headlamp, controls, fuel pump etc) ground out to.

When I test the engine chassis ground point (red lead to pos battery) it matches the voltage in the battery ~12.7, but when I test the powertrain ground point it drops to ~10v. Also If I measure any of the component ground connects (headlamp, controls, tail lights, fuel pump etc) it matches 10v. I'm assuming there is a fault somewhere in the powertrain component ground wiring, but not sure exactly how to search for it.

To add if I unbolt the powertrain ground from the engine block, and test the wire I get 1.544 volts. Does that mean it's grounding to the frame some how?

Not sure if this is relevant, but with the powertrain ground rebolted to the engine, if I touch the engine block or engine fins, I don't get any volt measurements, but if I touch the top of the engine, the chrome head above the engine fins, or any bolts, I get 10v readings...

Any idea how to resolve this?

Offline Bankerdanny

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Re: How do you find a bad ground?
« Reply #1 on: June 08, 2015, 12:31:58 PM »
I think you are doing it wrong. The black wire from the battery to the chassis is what makes the chassis the ground for all other components. When you test that connection as you describe you are effectively testing the quality of the cable since that is connected directly to the battery.

Disconnect the ground cable connection from the battery where it attaches to the frame and thoroughly clean the connector, the bolt, and the frame where it attaches with a wire brush. You can then test the ground quality by attaching the red lead to the battery and grounding against the engine.
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Offline ChopSticks

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Re: How do you find a bad ground?
« Reply #2 on: June 08, 2015, 12:40:58 PM »
What kind of results am I looking for? Good? Bad? And if I get a bad reading, what can I do the solve the grounding issue (assuming I've already cleaned it etc)?

Offline Bankerdanny

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Re: How do you find a bad ground?
« Reply #3 on: June 08, 2015, 01:05:26 PM »
Once you clean and reattach the ground wire you should get full battery voltage grounding to any nut or unpainted part of your engine.

The symptoms you describe in your original post just sound like a corroded connection between the battery ground cable and the frame.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline ChopSticks

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Re: How do you find a bad ground?
« Reply #4 on: June 09, 2015, 07:37:44 AM »
Yup was corrosion of the ground bolt that screws INSIDE the engine. sigh

Offline Bankerdanny

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Re: How do you find a bad ground?
« Reply #5 on: June 09, 2015, 08:01:42 AM »
At least you found it. Now back to enjoying riding season.
"The problem with quotes on the Internet is that you never know if they're true" - Abraham Lincoln

Current: '76 CB750F. Previous:  '75 CB550F, 2007 Yamaha Vino 125 Scooter, '75 Harley FXE Superglide, '77 GL1000, '77 CB550k, '68 Suzuki K10 80, '68 Yamaha YR2, '69 BMW R69S, '71 Honda SL175, '02 Royal Enfield Bullet 500, '89 Yamaha FJ1200

Offline 750cafe

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Re: How do you find a bad ground?
« Reply #6 on: June 14, 2015, 07:42:16 AM »
It never hurts to add an extra ground wire into the system.  ;)

Eric
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