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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10630
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I just purchased a used boat that has a Mercury outboard 85

Customer Question

I just purchased a used boat that has a Mercury outboard 85 HP. While I was running to boat, accidentally disconnected the battery. Now when I try to start the boat, it runs while I hold the key, once I release the key, the motor shuts off. What is causing this?
Submitted: 7 months ago.
Category: Boat
Expert:  Tan replied 7 months ago.

Hello. My name is Tan.

This could be a shorted key switch. We need to disconnect the black/yellow wire at the key switch or the switch box on the motor. Does engine run now? Be sure you have water to the motor and if it does start and run you will not be able to turn engine off. So touch the blk/yellow back to terminal you disconnected it from key in off position or touch terminal on switch box key off. The other option is to choke engine or disconnect the fuel.

Post back with findings.

Customer: replied 7 months ago.

I'm told I may have done something to the alternator or other electrical components on the motor, before I purchase anything how do I verify this? The boat is in the water, as mentioned if I hold the key to start position motor runs but if I try to give it gas it won't accelerate. When I release the key it goes to normal on key position and motors shuts off

Expert:  Tan replied 7 months ago.

The alternator is part of the charging system and has nothing to do with the ignition system. Now since the engine runs we don't have an ignition component issue as it runs leaving the ground circuit as possible issue. So the test I posted is to find the problem. Did you under stand the test?

Customer: replied 7 months ago.

yes I understand the test, so if I get the motor to run then the issue is the key switch do I have to replace it? Boat is a few hours away from me at the moment, am heading up later this afternoon and want to get use of the boat this weekend, appreciate your help

Expert:  Tan replied 7 months ago.

Correct. The key switch is the best place to disconnect the blk/yel wire as that narrows the issue to the key switch. It is possible you could have a short elsewhere. But if you disconnect at the key switch and this stops the issue the key switch is the problem. If engine continues to have the problem we will need to disconnect at the switch box to eliminate the possible issue.

From the description the key switch is the issue.

Customer: replied 6 months ago.
The ignition switch has a
It of wires soldered to it. Is there a way to disconnect the wiring at the motor. I've tried following the wires but I'm not an expert at engines. Where at the motor should I be looking for connections.
Expert:  Tan replied 6 months ago.

The black/yellow needs to be disconnected at the switch box on the engine.

Could I get the engine serial number please?

Customer: replied 6 months ago.
Where do I find the serial number
Expert:  Tan replied 6 months ago.

The serial number will be on the clamp bracket where the motor bolts to the boat.

Customer: replied 6 months ago.

Will I be able to get to it if the boat is in the water

Expert:  Tan replied 6 months ago.

That depends on how deep the engine sits in the water on this boat with you in the back of the boat. Are you sure this engine is a 1983 85 hp?

Does this engine have a distributor?

Customer: replied 6 months ago.
Not sure the year of the motor bought boat used
Expert:  Tan replied 6 months ago.

Sorry I have to opt out as I don't have the manual on this engine.

Another expert will step in if they have the info.

Customer: replied 6 months ago.

Ok so I need to do anything or will another expert be contacting me

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