outboard motor parts

DIY inboard outboard boat motor parts & accessories

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The electrical system of a boat can range from being fairly simple all the way to an electricians nightmare depending on the type of boat. This can be very discouraging to many people when troubleshooting an electrical system. One thing to remember though, is that most manufacturers pretty much stick to a standard when it comes to electrical system design. If you have purchased a used boat from someone that thought they were an electrical wiz, only to totally cluster any way of tracing a problem due to using whatever color wire they could scrounge up to replace or add an accessory, I really have no way to help you, but definitely feel for you because I have run across that problem so many times I felt like locking the doors and tacking a "for sale" sign on the front door. In this section we will look at some basic wiring diagrams and list some of the color coded standards that are common on almost every boat made. We will look at some of the electrical components on inboard/outboard motors and also some of the other boat accessories, and how to troubleshoot problems with them.

Motor Components

Other than the ignition components which are covered in the ignition components section, there are a few electrical items on an inboard/outboard motor that can cause problems.

Lets first look at the marine battery.

"Why bother using a more expensive marine type battery when an automotive type will work to start my motor?" Wrong!

Only the rich can afford cheap automotive batteries for use in a boat.....

To a degree the previous question is true, but there are some major differences in automotive batteries and marine batteries. Actually, a marine battery would probably make a better application than an auto type battery in your car or truck. Marine batteries are designed with more cranking power, more reserve power, and a deep cycle duty that will provide you with at least 150 deep discharge cycles if properly maintained.

People kill batteries faster than old age due to improper charging and maintenance! Recharge battery as soon as possible after discharge. Never allow a battery to sit for long periods in a run down state. Use an automatic charger only, with 10 to 20 amp output to charge marine batteries, and never overcharge.

The only other thing to say about a battery is keeping the cable connections tight and free of corrosion. If you disconnect your battery cables, make sure to NEVER cross cables to the wrong post. Connecting your battery backwards can instantly pop the rectifier in the alternator.

Starter and Starter Solenoid

A starter can be one of the most used and abused components on the marine engine. Besides being under constant attack of moisture and corrosion, a starter can undergo much strain, especially if something is keeping the motor from starting. For instance, if the motor has a "no fire" condition, and a person continually cranks and cranks with the starter in hopes that something in the cranking will fix the "no fire" problem, the starter is bound to practically burn itself up from the abuse. If your motor does not fire up within a few seconds of cranking it with the starter, stop and find out whats wrong. A motor in proper adjustment and good condition internally should never take but just a few revolutions to start and run. Starter problems can range from just plain being worn out, to corroded inside, to being burned up inside.

So you go to crank the motor and all you get is a "click" sound out of the starter. What could be wrong? First make sure your battery is in good condition, that there is no corrosion on terminals, and that cables are TIGHT! A loose cable connection can cause you unwarranted expense on replacement starters and batteries that were never bad in the first place. If you ever get water in the starter(submersed), replace it right then and there. It will probably still work ok for a while, but sooner or later its history and you'll be stuck on the lake, guaranteed! The easiest way to tell if the starter or solenoid is bad is simply to test system with a voltmeter. If you only get a click, attach negative lead of voltmeter to ground, and the positive lead to the yellow/red stripe wire on the solenoid. Try to crank motor. Does the voltmeter show a full 12 volts at the yellow/red stripe wire? If so, replace solenoid and starter as a pair. If not, the problem is not the starter. Trace Yellow/red stripe wire to key switch to make sure there is 12 volts to the switch connections.


The alternator is obviously for charging the battery during operation. Alternators come in different capacities, and are rated by amp output. If replacing an alternator, make sure that you replace with same amp rating. A very simply way to test an alternator, is to disconnect the positive battery cable while motor is running. If motor dies, the alternator is bad plain and simple.

Shift Detent Switch

The shift detent switch, figure 1 is a device that momentarily kills fire to the motor when placing shifter into neutral from either forward or reverse. If you pay close attention when shifting, you will notice a slight interruption in the fire of the motor. If this switch were bad or not present, you would most likely not ever be able to shift your boat into neutral no matter how hard you pushed on the lever. Its fairly rare that the switch itself goes bad. If you go to shift into neutral, and the motor dies, its almost a sure bet that your secondary shift cable is in bad shape. This is the cable that attaches to the shift bracket on the motor, and extends through the transom to the outdrive. To replace this cable takes some special know how, so it is recommended that you let a qualified technician take care of the job.

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Engine Compartment Wiring

Your boat may be equipped with a few accessories, or a lot of them. It is hard to cover them all, so lets basically say, that if the accessory does not operate, you simply need to make sure that a good ground and proper voltage is present to the accessory, and if it isn't, the accessory is bad. Always check the fuses and/or circuit breakers first.

Wiring would be a pain if manufacturers did not stick to a common standard. Figure 2 shows the standard wire color code, and lists what they are usually used for. Figure 3 shows the typical 8 cylinder engine wiring harness with electronic ignition system. Figure 4 shows the typical 8 cylinder engine wiring harness with conventional ignition system.

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Accessories Wiring

Again, there may be a few, or many accessories on your boat. It would be impossible to cover them all, so assuring that each accessory has correct voltage and a good ground tells you that it should work if it doesn't, and that the problem is the accessory itself, not a wiring problem. Rule of thumb, check fuse, check switch and breaker that operates specific accessory, check accessory, in that order. Electrical accessories fail due to being exposed to severe moisture conditions more than any other reason, so always check for corrosion at all contact points of a problem accessory. Wiring in the rest of the boat is also pretty much designed to a standard color code, especially the gauges and other items tied to the motor operation. Below is a table of most of the common wire colors, and their usage.
Color Most Common Usage
  Red Battery (+)
  Black Ground (-)
 or  Purple, Purple/White Stripe, Purple/Red Stripe Ignition circuit activated by key switch in "on" position
Yellow/Red Stripe Keyswitch to start solenoid
  Gray Tach circuit
  Pink Fuel sender
  Blue Dash panel lights
  Light Blue "Up" trim
  Green "Down" trim
  Orange Horn (Small) Alternator (Large)
Brown/White Stripe Trim sender
  Brown Bilge pump, blower, aerator, etc.
Black/White Stripe Bow light
  White Stern light
  Tan Temp sender
  Sky blue Oil pressure sender

Electrical troubleshooting can sometimes be a "hair puller", and if you have problems you just can't figure out, feel free to mail us, and we will gladly help you all that we can.