Mercury kill switch wires

[Jmcole3]

Just bought boat with 1999 Mercury 175. There doesn't appear to be a physical kill switch, but there are the usual black/yellow wires going to the switch box. I'm having ignition issues and it seems like the kill switch wires have been tripped. If I disconnect the black/yellow wire from 1 switch box, it starts by won't turn off using the key. If i disconnect only the other black/yellow wire from the other switch box, it will start and turn off, but no spark to starboard side. Any ideas how to fix this? Thought about installing kill switch but not sure how to wire it.

 

[Dave1027]

There is also the mercury tilt switch that may also be at play. You may also have bad wiring. I think it best to use an ohm meter and check the BLK/YEL wires for grounds. Disconnect the battery and turn the ignition switch on, then check the wires. It should be an open circuit to ground. Turning the ignition switch off should ground the wires.

 

[Chris1956]

I doubt you have a mercury (small m) switch on that motor.

The black/yellow wires are grounded at the ign switch to kill the spark. So if they are both disconnected at the switchboxes, the engine should run and not stop using the ign key.

So it sounds like one of them is grounding somewhere on your motor. trace them out from switchbox to ign key.

 

[Dukedog]

Thought about installing kill switch but not sure how to wire it.
after you get tha black/yellows straightened out you can install a "kill switch", between tha SOLID BLACK goin' to tha key switch and tha BLACK/YELLOW leavin' key switch.......

 

[Jmcole3]

I doubt you have a mercury (small m) switch on that motor.

The black/yellow wires are grounded at the ign switch to kill the spark. So if they are both disconnected at the switchboxes, the engine should run and not stop using the ign key.

So it sounds like one of them is grounding somewhere on your motor. trace them out from switchbox to ign key.

Thanks for the reply. I only see one black and yellow wire at the key switch. Any idea where the other one goes?

 

[Chris1956]

The keyswitch will only have a single black/yellow wire. It will run to a switchbox. The other black/yellow wire on the other switchbox will connect to it in the engine harness.

 

[Jmcole3]

The keyswitch will only have a single black/yellow wire. It will run to a switchbox. The other black/yellow wire on the other switchbox will connect to it in the engine harness.

If I understand correctly, somewhere along the line these 2 wires connect into the one going to the key switch? If I run a new wire from the key switch to the engine, I would need to split it to join the 2 black and yellow wires?

 

[Jmcole3]

So it shows resistance of 111

There is also the mercury tilt switch that may also be at play. You may also have bad wiring. I think it best to use an ohm meter and check the BLK/YEL wires for grounds. Disconnect the battery and turn the ignition switch on, then check the wires. It should be an open circuit to ground. Turning the ignition switch off should ground the wires

There is also the mercury tilt switch that may also be at play. You may also have bad wiring. I think it best to use an ohm meter and check the BLK/YEL wires for grounds. Disconnect the battery and turn the ignition switch on, then check the wires. It should be an open circuit to ground. Turning the ignition switch off should ground the wires.

It shows 111 ohms on both black/yellow wires with key on. Zero ohms with key off.

 

[Chris1956]

Well, the keyswitch is supposed to ground the black/yellow wire when off, so it should have zero ohms when off.

I think the 111 ohms is your issue. I would disconnect both black/yellow wires at the switchboxes and see what the black/yellow wire resistance with the key on.

 

[Jmcole3]

Well, the keyswitch is supposed to ground the black/yellow wire when off, so it should have zero ohms when off.

I think the 111 ohms is your issue. I would disconnect both black/yellow wires at the switchboxes and see what the black/yellow wire resistance with the key on.

When connecting to both black/yellow wires, I get 0. When connecting each one to ground, overload.

 

[Dave1027]

Like Chris said, you need to disconnect the BLK/YEL wires from the switchboxes. This way you are testing only the ignition switch and the wiring. Connect the black lead of the ohm meter to engine ground. Connect the red lead of the ohm meter to one of the disconnected BLK/YEL wires. With ignition off the meter should read zero ohms. With the ignition on the meter should read open circuit (max ohms). Then test the other BLK/Yel wire. Actually both BLK/YEL wires should read identical because they are connected together at some point.

As stated, above tests the ignition switch and the wiring. If that all passes the test then it's time to look at the switchboxes.

 

[Jmcole3]

Like Chris said, you need to disconnect the BLK/YEL wires from the switchboxes. This way you are testing only the ignition switch and the wiring. Connect the black lead of the ohm meter to engine ground. Connect the red lead of the ohm meter to one of the disconnected BLK/YEL wires. With ignition off the meter should read zero ohms. With the ignition on the meter should read open circuit (max ohms). Then test the other BLK/Yel wire. Actually both BLK/YEL wires should read identical because they are connected together at some point.

As stated, above tests the ignition switch and the wiring. If that all passes the test then it's time to look at the switchboxes.

Thanks. I'm ordering new switch boxes.

 

[Jmcole3]

Thanks for all the help. To follow up, I replaced the switch box and found a couple stripped wires. All is good..... for now.