Help troubleshoot gauges shorting out

Hi all,

I replaced all of my gauges earlier this year and had a problem with them shorting out. I got it all fixed somehow and they have worked on two outings. Last night I was attempting to hook up a depth sounder and they started shorting out again. Now without the depth sounder out of the equation, it still is shorting out.

Somehow I am getting voltage between the ground and the sender wires, different voltage on each one. This may be right, but doesn't seem like it is. Also, my nav light wiring doesn't turn on the lights, but does flip the needles all the way to the right. The last thing I did last night with all of the light wires removed and all of the ground wires removed, is hook up the voltmeter (worked), then the oil pressure (worked), then the fuel gauge (all three maxed out).

Obviously I have a short somewhere, but where? I really need to get this boat on the water this weekend, and don't want to spend another weekend working on it.

Any ideas?

Re: Help troubleshoot gauges shorting out

To Electrics, Electronics, (not engine)

Re: Help troubleshoot gauges shorting out

Sounds like you may have an intermittent open circuit, the opposite of a short. If all gages quit simultaneously, check for something they have in common---the ground connection. If the ground connection fails, the electricity will run through everything else in the circuit (other gages, etc) as it takes a different path to ground.

To verify this, you could try running a wire connected to a known and good ground to the back of the gages. Be careful not to make contact with any other exposed wires, though! If this fixes the problem, you have a loose ground connection somewhere. You could repair it or just run a new ground wire.

Re: Help troubleshoot gauges shorting out

All electric gauges are simply voltmeters graduated to display a level between 0 and 12 volts full scale. The gauge face is printed in whatever units are desired, and calibrated to the sender associated with it. The sender unit's resistance changes with the temp/pressure/resistance it's seeing, so the total of 12 volts is shared by the sender and gauge. In other words, at 1/4 tank of gas, the sender drops 9 volts, leaving 3 volts to the gauge. So it displays 1/4 scale.
That's why all your sender wires will be a different voltage.

Re: Help troubleshoot gauges shorting out

Okay, so taking these two responses into consideration, why would the gauges max out with the ignition on? It seems to me that somehow the ignition and/or nav light wires are somehow shorting out with the sender wires, sending full power to each of the gauges, and no power to the lights.

I wouldn't rule out the ground having a bad connection, but the gauges aren't cutting out, they are going to max readouts, so that doesn't seem like it would fit with your scenario.

All I did to cause the short last night was hook up the depth sounder to the ground and ign leads on the fuel gauge, which if I understand it right, should not affect the readouts. Also the depth sounder wasn't getting enough volts to turn on correctly, although it did work find connecting directly to the battery.

Re: Help troubleshoot gauges shorting out

That tells me you either don't have a proper ground that you're connecting the fish finder to, OR your IGN is not a full 12v, but in series with a/the gauges or sender. Does the gauge IGN wire actually go to IGN on the key?
Take some voltage readings to track it down.

Re: Help troubleshoot gauges shorting out

Not sure if this is related, but discovered my resistance wire is getting extremely hot. Tested it and came up with 1.2 ohms as opposed to the 1.8-2.0 it should be.

Any chance this is related to my gauge issues? Could it cause a voltage drop in the entire ignition wire?

Re: Help troubleshoot gauges shorting out

Examine the connections on your gages and look for loose wires or obvious shorts. Did your gages work ok before you replaced them? If so, check your work.

I don't know enough about the wiring on your boat to give you any more specifics, but I'd suggest connnecting a known GOOD ground to the ground connection on the back of your gages to determine if this is the problem or not. At least then you'd know, one way or the other. Connecting the ground of your gages to a good ground shouldn't be risky at all since they're supposed to be grounded anyways. Just don't let the ground wire contact any connections or terminals with voltages on them.

If this isn't the problem, then at least you have ruled out one possibility.