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.


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!!

Manitou Pontoon Boat Wiring


I am working on a 2005 22" Manitou Osprey Pro. Is there any source for obtaining a boat wiring diagram for this pontoon?

I just recently purchased this and have been trying to fix some electrical issues. Some are relatively straightforward.

Manitou Pontoon Boat

The pontoon's stereo speaker color codes matched the vendors color codes directly, but the stereo's power hookup did not - both yellow and red leads from the stereo were tied to a the pontoon's solid red wire. There was also a red wire with a yellow tracer in the same (stereo) wiring bundle of the pontoon but it was just clipped. Is one of the these a direct battery connection and the other one an on/accessory connection? The stereo wiring diagram shows two positive connections one labeled battery and the other labeled ignition - I don't want the stereo on all the time. The sun has faded all the indications of position for the ignition switch and all the switch/breaker functions. I don't even know if the ignition switch has an accessory function/position.

I don't know if the 5 function switch panel is a standard wiring. Is there a standard layout for the switches? Since the stereo speakers and power seem to follow the standard color codes for front -rear and power, is it safe to assume all the lights, horn and other accessories follow some standard of wiring? If so what are those standards and where can I find a standard schematic or wiring diagram for those standards?

I can't wait to get out fishing on this pontoon - it has an installation for a trolling motor battery in the console with direct wiring to an outlet mounted at the bow for the trolling motor (no battery installed yet) - there doesn't seem like a way to charge this battery from the engine's alternator/charger. Is there a way to connect this battery to the the engine's alternator but not allow the trolling motor battery to try to start the main engine? I don't what to run the higher gauge wiring for that. I just want to use the trolling motor battery for the trolling motor and accessories when the main engine is not running if that is possible.

I would like to develop a wiring diagram for this pontoon but I would hate to have to start from scratch and trace out the circuits by trail and error.

Any help would be really appreciated.


It sounds like a previous owner was doing some wiring modifications. We know the Manitou crew very well, and it is not like them to have hidden wires clipped off in their harnesses.

The key switch accessory position question is based on the brand of the engine on your boat. The easiest way to tell is to turn the key switch. It will either have 3 positions (OFF-ON-START) or 4 position (ACC-OFF-ON-START). If the key has an accessory position, it will have an A or ACC on a tab on back of the key.

There is not a standard layout for the switches on your helm. I would consider calling Manitou in Lansing MI to see if they have replacement panels for your boat that would have the proper labeling for the panels.

Here is the common boat wiring color code used by most OEM boat builders, including Manitou. You should be able to use this to trace down any wires on the boat.

If you want to charge the trolling motor battery while the engine is running, you will need to run some larger wires between the starting battery and the trolling motor battery. This wire size is based on the size of the alternator on your engine. Most VSR smart battery switch systems are capable of handling 125+ amps but the limit is the size of your alternator. If you alternator is less than 20 amp, the VSR is almost a waste of money. You will need to run your outboard at full alternator output for nearly 3 hours to replace what the trolling motor can draw in less than 1 hour.

Hope this helps,


Reset Revival

Hi Kevin,

I screwed up my boat wiring and hope that you can help.

I have a 2004 Sylvan 18 I/O. I had to jump it the other day and in my hurry I hooked up the boat battery cables in reverse. Push to reset breaker

I have power to the bilge pump, boat horn and navigation lights, but the other side of the dash has no power at all. This includes starter switch, bilge blower, and radio. I checked the fuses but found none bad.

Did I miss a fuse down on the starter?



Hi Maurice,

There is a push-to-reset circuit breaker on the engine that supplies power to the dash. It should be a red button about 3/8″ diameter on the stbd side of the engine near where the main engine harness plugs in.

Hope this helps,