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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10620
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I've got a 1974 mercury 402 40 hp. When I got it the wiring

Customer Question

I've got a 1974 mercury 402 40 hp. When I got it the wiring harness from the controls to the motor were trashed, I replaced the wiring and it ran great in the driveway. Then I put it on the water and it started, ran for 30 seconds and died. Now it won't start at all. No spark. I pulled the salmon wire on the switchbox and it fires up. That should be a ground fault in the kill circut from what I understand. I've replaced the choke switch, ignition switch, neutral switch, brand new wiring harness(boat side) both coils, and starter solenoid. But all were replaced after it quit running. I can't figure out where it is completing the kill circut
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hello. The salmon wire is shorting to ground somewhere in one of the harnesses. Have you replaced the engine harness yet?
Customer: replied 1 year ago.
I have replaced individual wires from the plug out that were dry rotted. But I have not replaced the whole harness. It ran after they were replaced and I can't find anywhere that's shorted
Expert:  Tan replied 1 year ago.
The only reason the engine won't start is no spark and that is caused by a short to ground on the salmon wire. That is the only thing it can be or a bad key switch.
Customer: replied 1 year ago.
So, I've re tested everything and it fires up with the orange wire coming from the switchbox disconnected. But with the motor running I have sparatic voltage on the orange wire, anywhere from 16 volts to nothing. It just bounces around.
Expert:  Tan replied 1 year ago.
That's voltage from the stator. It doesn't mean anything. That is the ground circuit. If you touch the salmon wire to ground it will shut the engine off. That is all that wire is for to kill spark.
Customer: replied 1 year ago.
It's the tilt switch, I've pulled it loose and function tested it with a meter three times and everything checked out. But when I disconnected it everything works.
Expert:  Tan replied 1 year ago.
Ohm tests don't work for the tilt switch, kill switch or the key switch. The tilt switch is another path to ground just like the key switch. Any path to ground will cause no spark. I would just eliminate the tilt switch. No one uses these anymore.

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