Goner Gauges


I have a problem with dead gauges on my old aluminum fishing boat.

Last year the tachometer and gas gauges were the only two working. The speedometer, trim gauge, and volt meter did not work. As the year progressed, the tach started to stay in one place and the gas gauge stopped all together.


When looking at the connections for the gauges they are plugged into the back of the gauge except for the gas gauge which was replaced two years ago and it has wires connecting it to the boat wiring harness. I have checked and replaced all the fuses and looked for any loose connections that I could see.

What should I look for now?

Thanks for your help.


If they are all dead, it is probably a bad power or ground connection.

Using a meter of a test light you should be able to measure 12 volts between the purple and black wires on all of the gauges when the key is on.

Since this is an older boat, the speedo is probably a pitot style that works off of water pressure. Check the pickup on the transom to see if it is plugged.

Hope this helps.


Nitro Nuisance

Boat Wiring Guys,

I need your help with a 1997 Nitro 640 LX fishing boat that I just purchased.

Nitro 640LX

When I put the red/green navigation light into the plug in base at the bow, it doesn't come on, but causes one of my gauge lights to light up and stay on.

Any thoughts on where this might be going wrong?



The ground wire for the dash panel area is no longer connected. Because of this, the dash is grounding through the filament in the red/green light.

Run a test ground wire from the battery negative to any ground at the helm (maybe a gauge) to confirm.

Hope this helps



Thanks for the quick response,

You were right about the ground wire. We found and fixed that, but we have another problem now.

There is a large wire with a plug that goes into the motor that there is apparently a short in.....when we turn the ignition on, it will not do anything sometimes until you move that large wire around.

What is that wire called that plugs into the motor and apparently goes to the switch as well?

We need to figure out what to get to replace it.

Thank you,


It sounds like it is your main engine harness plug.

Most of those are modular and can be taken apart. This means that you may be able to just replace some terminals instead of replacing the harness.


Bass Boat Gauge Dimmer

Fishing Boat Wiring Guys,

I really appreciate all of the work that you guys put into your site. I'm guessing that it has kept loads of boater from doing very stupid things.

Tracker 175TXW bass boat

Here's my question...

I have a 2013 175TXW Bass Tracker and would like to add a dimmer switch to the instrument cluster lighting.

Could you tell me what color is the power wire for the lights? Or are the lights powered off the power wire for the individual gauges?

Any info would be helpful.


According to boat wiring color standards, the lights should be powered by the blue wire. But, I would recommend that you test with a meter before cutting anything.


Chopped Charger

Hello Kevin,

My fishing boat wiring includes a Guest 2611a Charge Pro Boat Battery Charger. It has worked great for years but I need your help to get it charging again.

Guest 2611 Boat Battery Charger

During a recent vandalism at my marina, the charger's A/C cord got cut off.

Could you please tell me how to reconnect everything? That is, I need to know what wire is what color. There are four wires altogether.



I'm sorry to hear about your problem. The good news is that it shouldn't be too hard to repair.

The Guest chargers use the international wire color code. So in your case...

  • Brown - AC hot - to your black
  • Blue - AC neutral - to your white
  • Green - ground - to your green or unshielded

Hope this helps,


Shiver Me Trimmer


Tonight I ran into a very odd boat wiring issue.

I have a 2002 Proline Sport 20CC with a 150hp Mercury outboard. Traveling along in the fog, my motor started to trim itself up and out of the water - all by itself! One thing I noticed is when the motor would trim up the bilge pump came on as well. (No water in the bilge, by the way)

Proline 20 CC

My guess is a common short.

What should I look for in tracing this short?



It could be a ghost. It is that time of year.

BUT, it is probably a short between the trim power wire (red) and trim up wire (blue) and bilge power wire (brow) near the shifting mechanism on your helm.

It is common for wires to be pulled tight to the shift cables. They have some movement when the shifter is actuated and eventually wear through.

Hope this helps,


Haha funny you say that. With the fog rolling in, the lack of visibility, and the boats mind of its own it was like out of a horror movie! I was waiting for a pirate ship to pull up out of the fog! Lol

Anyway I did some troubleshooting this morning and found the trim switch on the motor was passing power through it on the up side even when not depressed. Luckily the problem happened while I was troubleshooting. When I press the trim up on the motor and let go it would continue to trim up for a second before stopping.

When checking with a volt meter. Trim up pressed would pass about 12.6v and when let go would go down to 12.3v and slowly trickle down to about 11.3v. Up side was fine and passed no power if not depressed. So I disconnected that switch and only used the throttle trim switch and it was responsive and stopped without delay when I let go of the button. So it looks like a bad trim switch at the motor.

But it doesn't explain why the bilge came on too, lights and fish finder flickered when that happen also. I left the motor's trim switch disconnected so I guess only time will tell if that was the only problem.

Thanks for your help! I appreciate the quick response and assistance!!

Tach Fuel Connection?


I have 1992 Smokercraft Pro Mag, with a 1992 Mariner 90HP two stroke oil injected engine. I bought the boat used about 2 years ago.

At first, the tachometer and the gas gauge were working fine. But, now neither one of them does anything whether the engine is running or not.

Smokercraft Logo

The tach does not "flatline", instead, it is reading somewhere in the middle of the dial regardless of whether the engine is running - or if the key is even in the ignition.

Do you have any idea how to fix this?

Are the two gauges on the same wiring or the same fuse or circuit? I have not tried to do anything to fix them yet, but it is becoming a real pain to operate the boat without a gas gauge, always guessing at how much is in the tank.

Thanks for any assistance you can provide.


 Both of the gauges are powered by the same wire.

  • Power for the gauges will come from the purple wire.
  • Ground for the gauges will come from the black wire.
  • The source of the purple wire is the key switch.
  • The dash will have a common ground.

This should be easy to fix,


Shock Absorber


I’ve heard in the past and as recently as last night that “dc won’t shock you”.

Well, I’ve grabbed a plug wire at the plug and can report to you that the DC electrical system is standing tall. I had a brain fart prior to grabbing that wire.

Electrical shock hazard

But as to the truism, maybe I am missing something? What are these people talking about?

Please explain.



As you proved through your careful experimentation, DC can shock you. The determining factor is whether or not the voltage is high enough.

Boats run on 12 volts (some at 24 volts). Your internal resistance is too high to allow for a noticeable discharge through your body. But, on an ignition system, the DC voltage can be as high as 30,000 volts. (2,500 times as high as your normal boat wiring). It is easy to discharge 30,000 volts DC or AC through a body.

Hope this helps to clear things up.


Shore Power Concerns


I just found your site, Thank you! There is a lot of useful boat wiring info here, especially for those of us who are not near to nor have access to a marine or ABYC electrician.

Hopefully you can help me with my questions, there are a few.

Dockside AC Pedestal

I have a 1998 Grady White 272 Sailfish which did not come with shore power, only the usual marine electrical components, pumps, refrigerator, wash down, macerator, etc. The boat is currently on a trailer in my driveway until I finish repairs and I am sure it is safe to put back in the water.

After reading Charlie Wing's book and numerous online articles I added shore power. Starting at the transom with...

  • 30 amp stainless outlet, to 30 amp double pole breaker within one foot of outlet
  • Green ground to galvanic isolator then
  • All three marine grade 10gauge wire goes twelve feet to cabin where it
  • Connects to a Blue Seas AC panel #8409, double pole disconnect with amp/volt meters, reverse polarity indicator and three 15 amp circuit breakers.
  • Black to hot, white to neutral, green to ground.
  • 1st circuit to GFCI outlet in head (12 gauge wire)
  • 2nd circuit to GFCI outlet in galley (12 gauge wire)
  • 3rd circuit to Pro Mariner Pronautic 1240P battery charger (14 gauge Wire).
  • Wire from 40 amp charger to batteries 6gauge. with 50 amp fuse each line.

Now for my questions.

  1. I do not have a negative ground bus in the aft compartment which contains three batteries (1 house, 1 each for the outboards), switches, charger, main wiring for the outboards. Each outboard negative. goes directly to it's own battery. Charger instruction's want the charger case stud attached to engine block or DC ground buss with wire no more than one size smaller than charging leads. Since the only negative ground bus is under the cockpit controls (dashboard) and it would be difficult to run this wire to the outboards, can I connect the case ground of the charger directly to one of the battery negative terminals (All battery negatives are connected together). they all end up together anyway don't they?

  2. If I understand correctly, ABYC code wants DC negative connected to AC ground (green). Can I use the battery negative terminal and wire to ship side of the galvanic isolator? Again it seems however these wires are connected they still end up together. If this is acceptable what would be the correct size wire from DC negative to the AC ground?
  3. Here is the strangest question I have for you. It makes no sense and would seem impossible.

    When I take a voltage measurement between the hot wire and neutral, or hot wire and ground at the GFCI, all is correct at 117v, but when I test hot to anywhere on the boat be it a screw which is not touching any metal only fastened into wood or fiberglass, a hose clamp around a hose to toilet, the DC refrigerator frame, or just the fiberglass or gelcoat I get voltage readings.

    With the hot lead of the volt meter in the hot side of the outlet and the negative side of the volt meter touching a screw (screw is only into fiberglass I took the wall apart to check ) I am getting a reading of 60+ volts. As I test screws further away from the outlet with the negative, the voltage reading drops. Just touching gelcoat the reading is around 20 volts. This happens at all outlets.

    I also tested the outlets with a GFCI push button tester, lights lit up properly and the circuit tripped when the button was depressed. What do I have incorrect or what could be causing the voltage readings? Thank you


Those are excellent questions about a subject that warrants a lot of concern because of the risks involved. Here are my thoughts on each of the three.

  1. Yes. The battery negative chain would be a great common ground.

  2. My preference is to run a 10 AWG green wire from the galvanic isolator to the AC ground bus at your AC panel.

    From the AC panel ground bus I would run a 10 AWG green wire to the DC negative. In your case this is either the bus under the helm or the battery negative.

    Since the greatest chance of an AC fault is from AC hot to AC ground I would rather have the fault path more direct (to the panel, through the GI, and to the dock) instead of back to the AC panel, to the DC negative, and then through the GI to shore.
  3. I asked a friend of mine for his opinion on this one and I believe that he may be right. The crazy readings may be from the high input impedance of the voltmeter. As soon as a load is added to any of these circuit combinations (AC hot to screw) the voltage should drop to zero.

Trolling Plug Work Around


I am in need of your help with my boat's 24 volt trolling motor wiring.

I have a problem using my 70 lb. trolling motor at full power. It shuts down and I cannot use it.

Marinco trolling motor plug

The motor is wired using a Marinco 24 volt plug and receptacle. I talked with Marinco at one time and they told me the jumper in the plug was under sized but they had no corrective parts.

Any ideas of what has happened or what I can do to get this system running again?

Thanks for your help!


One option is to use only two of the terminals in the Marinco plug and do the 12/24 jump at the battery.

Basically, there is a wire from the plug to the negative of Battery 1 for the ground and a wire from the plug to the positive of Battery 2 for the 24v positive connection. This lead has circuit protection at the battery. A jumper between the positive of Battery 1 and the negative of Battery 2 is added to create the 12/24 system. This wire should be made from the same size wire as the long trolling motor leads.

Hope this helps,


Crest Crisis


I have a Crest 2003 Family Fish Pontoon with a 75 HP Mercury engine.

Recently, the 20 Amp Starter/Accessory/Trim fuse began to blow. I took the boat into the dealer where it was purchased and they spent ~$400 to tell me that the engine wiring was A-OK, but they could not fix the problem.

Crest Pontoon Boats

The hardest part is that the fuse will not blow unless the boat is in the water. I have tried to duplicate everything leading up to the blown fuse while running the engine with a water hose connected and have not been able to get it to fail. Then I put the boat in the water and 10 to 90 seconds later (after putting it in gear), it blows. I lose the instruments, trim, but the engine continues to run fine. If I shut down, I can not restart without replacing the fuse.

I tried on land to ground the pontoons to see if that was it. Then I sprayed water on the wiring from the engine to the controller (rests on top of a pontoon). I removed the gas level transmitter. I removed the live well pump. I tried everything I could imagine.

I know this fuse enables power to the starter relay, and the up and down trim relays. They were checked out by the shop and found to be OK. I also measured the running voltage on the rectifier at 14.8 amps with the engine throttled up. The boat is simply instrumented: Tach, voltmeter, fuel gauge and that's it.

Sure could use some sound advice.

Many thanks.


At the key switch, disconnect all wires connected to the A or I terminal. These should be purple. This will cut power to your gauges and anything else connected to the key.

If your key switch is incorporated with your shifter look for the purple wire coming out of the control. The motor will start and shut down without a problem.

If the fuse still blows, look for a bad spot in the wiring between the engine and the key. If it doesn't, then the problem is in one of the accessories connected to the key switch. It could be something as crazy as your stereo or tachometer.

Hope this helps


Marine electrical advice for fishing