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Charles
Charles, Marine Mechanic
Category: Boat
Satisfied Customers: 3618
Experience:  US Navy (Ret) Certified Mercury Marine Tech with over a decade of repair experience.
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2000 4.3 v6 mercrisier will crank up fine with ignition

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2000 4.3 v6 mercrisier will crank up fine with ignition switch but will not turn off with switch. Also. The electronic fuel pump will not stop running. Runs all the time even with switch in the off position. Have to unplug pump to get it to stop running. At the same time the automatic choke on my carb gets very hot to the tuch

Hello, my name is***** will assist you.

Do you have a multimeter and know how to take basic voltage measurements?

Customer: replied 1 month ago.

Ok, different boat manufactures use different color wires, but on the back of the switch there should be a red, and a purple, a yellow and a black. With the key off, see if there is power to the purple or yellow wires. you are looking for around 12V. Use the black as the ground

Customer: replied 1 month ago.
I took the alternator off and had it checked. Alternator works fine
Customer: replied 1 month ago.
I am not at my boat right now but I have tested the wires. They have the correct voltage on them

With the key off, there should not be any on them. That is why the engine will not turn off. You have a bad key switch.

Customer: replied 1 month ago.
I am pretty sure it is not the ignition switch. I just took the wires off of the switch and the purple wire going to my carb choke is still hot while unplugged from my ignition switch. Fuel pump runs all the time.

Unplug the connector between the engine and the boat. See if the pump still runs or not. You could have a stuck relay on the engine.

The key switch would be the most common issue, that is why we start there.

Customer: replied 1 month ago.
I unplugged supply from boat to engine. Pump still runs. Automatic choke still getting power through purple wire. With ignition in the off position yellow wire(solenoid) no light. Purple wire(ignition) light is off. In the off position the red/Purple wire from Battery light is on. I only have three wires to my ignition

do you have the serial number of the engine handy?

Customer: replied 1 month ago.
Ol648517R2
Customer: replied 1 month ago.
2000 mercrusier v6

The engine serial number wil be on the flame arestor on top of the engine. It will atart with a number, then a letter, followed by 6 more numbers.

Customer: replied 1 month ago.
Will get the number in the morning

The first one was it, I just needed to separate it.

On top of the engine you will see a solenoid with 2 large wires and 2 small wires. test both the large posts with the key off and make sure that only one has power to it. If that is good, unplug the ECU and see if the fuel pump will stop.

Customer: replied 1 month ago.
What is the ecu?

That is the brain on the engine. It should be mounted to the right side exhaust manifold.

Customer: replied 1 month ago.
Only one wire on the solenoid was hot. I unplugged the ecu. Pump still kept running

You have a short in the main engine wiring harness. You have already eliminated the key switch and boat harness when you unplugged the engine. Unplugging the ECU eliminated it. The only thing left is the harness has to be shorted someplace. Look for a worn or burnt spot on the engine harness.

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