Electrical question

[rail bird]

I am trouble shooting and making repairs too my boats 12V DC system. The main problem started on the water last year when I turned on my navigation lights and noticed that all my gauges pegged Gas, Tach, Oil, Speed, Temp. When I turned the lights off the gauges returned to normal. My boat is wired with lighted gauges, so they share the circuit with the navigation lights and unswitched 12V feeds the gauges from the ignition.

If I disconnect the power on both sides of the gauges one at a time they should look like an open circuit between the the light power and the guage power, Is that correct? Any other spots I should be looking? I am going though the curcuits one by one to isolate the issue.

Thanks for any help

[Trolling82]

it affects all the gauges????

that's a bit odd. Do the gauges light up as well?

If they don't, it sounds like the feed for the gauge lights is going directly to your gauges signal wires.

Would have to see how you have it wired. I was an electronics specialist for F-15s in the AF so I'm a wiring fanatic but I'm a visual person.

Probably best advice is just trace it out. find where the juice comes from nav light switch and goes to gauges. follow it and make sure it's all hooked up right. Then check your grounds.

Open circuit for light power on gauges when nav lights off. Closed when nav lights on. Gauge power should be faint closed circuit with key on. Gives the gauge reading depending on amount of power going to gauge.

[Trolling82]

Oh and you should always have an open (no continuity) circuit from gauge power to light power.

make sure the light power doesn't have any jumper wires running to any gauge powers....

It's not going to be a circuit located right at a gauge I would doubt.

Wait. this happened all of a sudden with no wiring done to have changed it? Check grounds.

5-1 says you got a bad ground somewhere!

[FSNmachine]

Check your grounds. If you lost ground the current will try to seek a path to ground and this could cause this type of symptom.

[Trolling82]

Just thought of one more thing to help isolate it. Disconnect the light power from a gauge. MAKE SURE IT DOESN'T COME IN CONTACT WITH ANYTHING! Then turn nav lights on. Check to see if the rest of the gauges still peg. Turn nav lights off. Reattach light power to gauge. Continue this with every gauge. Possibility one gauge you disconnect will not make the rest peg. Possibility that gauge has an internal short or bad ground.

[Gezijamez]

The gauges have 2 seperate circuits, the sending units for each are what make the gauges display info,(like temp.oil pressure and so on) lights are a seperate circuit, could be lights for gauges are getting ground tru the gauge,instead of a separate ground, try runing a wire to the ground side of the lighting circuit to see if this eliminates the problem. also, also check voltage to the lights, if you are using 2 batteries you may be feeding double voltage to the lights. I would think by the sound of the problem you may have a loose ground in the lighting circuit. hope this is some help.

[ray koziatek]

ill 2nd the ground the 3 wire plugs to the guages hava ground one is probly dangling just a bit... I had same problem about a 30 sec fix

[rail bird]

Thanks for all the ideas, I pretty much have everything apart at this point because some things needed to be cleaned up anyways. The gauges themslves were hard wired with nut and post at the factory. It may be that one is shorted out causing the problem or the ground. It has taken me awhile to trace out the grounding system on the boat and I have not found all the connections just yet. Some were crimped together so I am going to put those to a buss.