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Slidertater
10-07-2010, 11:56 PM
I don't know if this is the correct forum to ask this question but I will give it a shot.
My newly acquired 1990 Donzi GT 250 has an electrical issue.
When the boat lights are on every time i key the mic on my VHF the boat lights dim.
In fact the boats lights dim when ever I use anything powered by the boats electrical system. This happens whether or not the engine is running.
The batteries are staying charged by either the alt when running or the 120v shore power charger.
I think I may have a ground issue but have no idea where to start to look for the cause of the problem.
Any help would be greatly appreciated.
Thanks george

Planetwarmer
10-08-2010, 12:34 AM
I am going to say that you need to replace the negative ground cable to the battery, and clean all contacts. You might as well replace the positive cable as well. Another way to check if it is a grounding issue, is take an alligator clip (like a jumper cable or something) and run it from the (-) side of the battery and connect it to the back of the Tach on the (-) pole. It seems on my boat that all the (-) is connected to the (-) pole on the Tach. I did this, and figured out I had a ground issue. Its a good way to bypass all the potential problems and begin narrowing it down from there.

This worked like a charm, and I then KNEW I had a grounding issue. I fixed the problem.

gcarter
10-08-2010, 06:43 AM
Definately a grounding issue.
It's frequently a problem w/production boats w/a few years on them.
It's often useful to add a ground bus somewhere under the dash and lead all your grounds to that.
It'll require a little re-wiring, but it'll do wonders for the electrical system.

MOP
10-08-2010, 07:16 AM
I bet you don't have a clean power circuit for your accessories! Common most just take power from where ever they can under the dash, 99 & 44 100% of the time they take power from a #14 wire. Very few small boats have a bus bar at the helm with #10 wire for both power and ground fused at the battery, electricity is very much like water it needs a large enough wire/pipe to flow enough to power the extras.

zelatore
10-08-2010, 11:30 AM
I bet you don't have a clean power circuit for your accessories! Common most just take power from where ever they can under the dash, 99 & 44 100% of the time they take power from a #14 wire. Very few small boats have a bus bar at the helm with #10 wire for both power and ground fused at the battery, electricity is very much like water it needs a large enough wire/pipe to flow enough to power the extras.


I'm going to place my bet with MOP. I'm assuming the VHF isn't stock and it was added by some previous owner. Most Average Joe's don't know squat about electricity beyond red for positive, so I'd bet they just found a hot wire and spliced into it.

But after that, I'm also be highly suspect of a grounding problem. People also tend to forget electricity is a round trip, and just as you can't simply keep tyeing more loads to a given hot lead, you have the same issue with ground leads.