"O/D = Out Drive The ground c
"O/D = Out Drive The ground connection is a stainless wire connecting the outdrive to the engine on the inside of the transom to complete the electrical circuit for the trim switches on the outdrive since the engine block is the ground basis for the electical system. It is there more as an insurance policy that there is always a ground circuit even though the engine and O/D are connected metal-to-metal with a variety of moving metal parts.
A hose clamp on the barrell plug could be part of your problem. The engine part of the plug is the female segment. The split pins are molded in poly/rubber designed to keep tension on the split female segment of the plug. Inserting the male part of the plug completes the connection but requires a certain amount of tension to maintain electrical continuity. If you are having to clamp the two together because they can not remain connected, then the plug has seen its useful life. The squeezing action of the clamp may actually be interfering with the plug's job by causing the pins to separate under the clamp's tension. Remove the clamp and double wrap the barrell plug with 2" wide 3M electrical tape.
Replacing the wire harnesses is relatively simple if you get the correct one. All of the wires are labled except for the large 6-8 ga. black negative (-) ground and 6-8 ga. red positive (+) primary ignition wire that attaches to the fuse buss bar or in some cases directly to the ignition switch using an in-line fuse.
I replaced mine this last July due to 19 yrs. age and corrosion. I purchased a 12 ATC fuse block that uses automotive type bayonet fuses. The main ignition fuse I replaced with an automotive 25 amp autoreset circuit breaker. All you do is connect the larger red wire to the positive post and the black ground to the negative post. Your individual circuits for lights, pumps, horn, livewells etc. can be controlled from the main fuse panel just by connecting the hot wire to the hot (+)side of the fuse box and the negative (-) to the ground pins. Then insert the correct amp fuse in the circuit. Note that the ground pins are grouped together while the hot (+) are set in a row. Most Nav. and anchor lights, blower, horn and bilge are either fused at the switch or have an automatic breaker next to each. If you replace any circuits that are not included as part of the harness, use the correct ga. and same color wire for safety and ease in trouble shooting. Most boat circuits for lights and fans use 16 ga. wire unless their amperage requires a 14 ga. Never use any color but black for negative (-) ground circuits. You'll find that PURPLE is the most common color used in positive circuits in a boat harness. Blue is the color used on gauge lights. Yellow w/red stripe is power to the ignition relay from the switch. Some wires in newer harnesses are not used. Do one wire at a time with the battery disconnected.
I like to seal the connectors with liquid electrical tape on gauges, fuel, oil pressure, engine temp sending units and other connections to lock out moisture. Use especially where the wire is crimped and you see a little bit of the copper wire--coat it to seal it. Use sparingly, you are not painting a house. For connecting two wires together, use a crimp connector that has heat shrink tubing on it.
Think of corrosion in a wire like a wick on a oil lamp. The corrosion starts at the end and wicks its way inside the insulation where it can't be seen. Starter cables are notorious for this condition due to the acid from the battery. If you see greenish corrosion on bare copper wire, it's definitely worked its way along the wire increasing the resistance of the wire.
In a salt environment, tinned wire is available but costs more. But it reduces corrosion problems."
