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ground issues

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So weird grounding issues. I was troubleshooting my gauge 4n1 and I started to notice a weird floating ground as I was running tests. So the run down is when I turn on any device on my blue seas ground and power bus my ground starts to float. If I turn the interior lights on I still have a good ground. I haven't tested plugging something into an accessory to see if that causes noise on my ground. But for obvious reasons this affects my gauge cluster. Any advice to help me troubleshoot this.

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Its a 4awg from a perko switch in observer storage

What about the ground, 4 ga also? 4ga seems small to feed the helm, 3 amps, a ballast pumps, ect. Have you done a voltage drop test on the cables?

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So the ground comes off the under dash ground bar. I need to redraw the circuit more clearly. But with the stereo off and the pump off. I have issues with the ground when just pp is on.

On ground bus fed by a 4foot 8awg from the under dash ground bus

Perfect pass




On the power bus




1of the amps power comes straight off the perko

Pp is powered off the ignition circuit

With pump and amps and ws420 off and only pp on when the key is flipped to ignition I get noise on the ground.

If I disconnect the blue seas ground bus or no devices on the blue seas ground bus are powered I have no noise.

If I just turn on the stock lights I have no noise

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Batteries to perko is a short run for me since its all under observer. Not sure what awg is there. But to my starter at the back of the boat I run 2/0.

Could my front ground bus under the helm be floating? I moved the batteries from the rear locker to observer last year. I only run one 2/0 to the back and that is connected to the starter. Is there another ground I need to connect to in the back.

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YES. The batteries need to connect positive to the starter and ground to the block. All circuits should have the same gauge wire on power and ground (it's a circuit... a loop). The grounding point on the block is on the back of the motor, above the transmission, if memory serves.

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So I have common ground from my battery to my bus under the dash.

Weird things.

I have a wire on my ground terminal at the batteries run over to the dash for testing.

Any time I turn any device on I get a build up of resistance between ground from my battery and my under dash bus. I measured voltage drop with stereo blower lights and pp on and its around .23 volts. If I check my resistance between the plug for my computer and the battery ground its very close to the same as with no devices on. I'm tempted to just splice the ground reference on the computer with a straight run over to my batteries.

Edited by jhartt3
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Oh, boy. It's hard to know where to start with this. SD has you on the right track, but I have a few random questions and comments.

1. What do you mean when you say, "ground starts to float?" How are you measuring this, and against what reference?

2. Which Blue Sea device do you have, and how do you have it wired?

3. When you ran the jumper from the batteries to the dash for testing, what gauge wire is that one, and how are you using it?

4. When you measured the 0.23V voltage drop with stereo, blower, lights, and PP on, where did you place the meter's test leads do do that? If you really did measure the drop across the 8 Ga. ground wire, then you have approximately 91 Amps running through that wire (assuming a healthy 8 Ga. copper wire with perfect connections that has 0.6282 Ohms per 1000 feet). I suspect that you may also have some dirty connections. Does the 8 Ga. wire get hot when all the stuff is on?

5. Are you testing resistance with anything powered up, or are you removing things from the circuit to test resistance? Testing resistance of a device is nearly worthless anyway unless you are measuring the voltage drop across the device and dividing by the current through the device. Also, your meter's resistance measurement (Ohms) is not able to work properly in a powered circuit, because the meter assumes that it provides the only power during the test. I can assure you that your blower draws a lot more current (has much lower resistance) than your PP does.

Rather than splice a new ground from the computer to the battery, just replace the 8 Ga. wire from the under dash ground bus with something much more substantial. Since you have amps returning to that point, consider moving those grounds to the same place that their power originates. Finally, go ahead and replace your engine ground with something substantial as well.

By the way, the stock lights probably improve the ground because of their low resistance. Even if they are on the crappy ground as well, they lower the amount of difference you can have between the positive and negative sides of your circuit. You didn't mention if you also have a gob of LED lighting wired to the under dash ground point, but the controller for those will create plenty of noise on your circuit as well. Those will be their own topic of discussion.

Good luck!

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gonna try to answer all these

First the setup was a 10awg wire run from my battery negative terminal so i had good negative to test against under the dash. I tested from that wire to my bus and it was 2 ohms so should be good, this was with nothing on.

I turn on any device and there are 300-400 ohms on the ground from the battery 10awg to my ground bus and every time i add another device the resistance builds another 300-400 ohms. This doesnt stop any of my devices from functioning besides my computer which needs a good 0 ground reference to accurately get the temp, oil pressure etc.

1. so when i say ground start to float i mean i have resistance on there when measured by my meter with devices on.

2. i have the blue sea/perko dual battery setup. and a blue seas power and ground block. the blue seas dual battery/perko is wired per the manual. and the power/ground block has a 4awg power wire from the perko on the accessory side and a 4 awg from the ground block under the helm.

NOTE: what is the factory wire gauge to the ground block under the helm? the largest wire i see there is 10-12 awg. i plan to add a 2 awg from the motor to the ground block under the helm

3. the wire going from the batteries to the dash is 10 awg and i am using it as a ground reference. with nothing on i test between the black and tan wire on the plug to the computer. i get around 950 ohms. i test between the tan wire and my battery ground reference and get the same. as i turn devices on the difference between the black and tan wire drops dramatically. but the resistance between my battery ground reference and the tan wire remains in the same ball park.

I also use this wire as stated above to test continuity between my helm ground bus and the battery refference. i have tested this as stated above and it consistently adds 300-400 ohms per device as measusred when i go from my battery reference to my ground bus

4. i measured total drop of the whole system. I measured from the ground reference at my battery to the 8 awg wire at my blue seas ground bus.

5. i test it both powered up and unpowered. and see the resistance grow as i turn devices on.

I'm not sure where my ground bus under the helm is getting its ground. there is only the 2/0 ground wire on the engine in the back that i installed there is nothing else back there that i can see.

ordering a 2awg wire to run to my ground bus at the front from the motor at the back hoping this solves everything. we will see..

open to any advice right now to get this running

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i have the blue sea/perko dual battery setup.

What is this exactly as those are two product manufacturers? A blue sea what as in a model and a perko what as in model. Also, is the blue see referenced here the same blue sea product in the diagram?

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Ok so you have nothing perko at. The standard perko switch is quite different from the Blue Sea Dual Circuit Plus switch that comes in that kit. This makes huge difference on power flow and diagnostics.

Amps need to terminate to the switch, on the terminal that corresponds to which ever battery you designate as the "house" battery.

Amps need to ground directly to one of the batteries.

Your need fuse block/gnd combo needs to run to the switch for the B+ fuse feeds and battery ground direct for the ground feed.

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Even if I disconnect the 4awg ground that goes to the negative bus on the blue seas block. And connect pp directly to my helm negative bus I still get increased resistance on my ground circuit

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Again, you cannot use an Ohm meter in an active (powered) circuit. It won't give you any meaningful information, and can blow your meter.

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well i went ahead and ordered a 1/0 ground cable to run to my helm bus. See if this give me a better ground up there. I may end up splicing a str8 run to my computer ground if it still is getting noise on it from other devices being powered up.

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Ok so i ran a 1/0 ground wire from the engine ground to the helm bus and this created a solid ground. My plan is to segregate my blue seas bus using the 1/0 and use a 2awg from the back to the helm. this will get me a consistent good ground reference on my plug to my PC. Now here is hoping the PC is still good.

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