1985 40hp ETLK

I bought a Lund boat with twin 40 hp as the factory setup. The first thing I did was purchase the service manual. Then, I cleaned the carbs serviced the lower unit with new impeller kit and seals, replaced aged fuel lines, and serviced the electric trim as the fluid looked awful. They run great with great, even compression on all cylinders in both engines.

My only problem is that I can't get one of the engines to send a tach signal to the dashboard tach. If i switch plugs, I can get the other outboard to work on the other tach, so I know it is from the motor to the control.

While I think I do a pretty good job on the mechanical stuff, I never studied electrical and am really stumped as to where to begin. I figure that if I test the wrong thing or unplug something and try to run it, I could probably wreck something in the system. I can run with it the way it is, but when both are running, with my hearing, the tach is going to be the best way for me to see if something is going wrong before it totally quits.

Can anyone help direct me to a particular place to check? I have checked every connection on the engine and verified that they are connected tightly.

Thanks, in advance, for any and all help.

The green wire from what Yamaha calls the "lighting" coil is used to provide the tachometer RPM signal. There are several connectors along the way from the lighting coil to the green wire that is in the ten pin harness. The connections in the ten pin connector as well. The connections from the control box to the tachometer. I would inspect all of those connections. Plus the wiring itself.

You can see these connection points in the Yamaha service manual. One diagram for the engine connections and one diagram for the instrumentation.

boscoe said:

The green wire from what Yamaha calls the "lighting" coil is used to provide the tachometer RPM signal. There are several connectors along the way from the lighting coil to the green wire that is in the ten pin harness. The connections in the ten pin connector as well. The connections from the control box to the tachometer. I would inspect all of those connections. Plus the wiring itself.

You can see these connection points in the Yamaha service manual. One diagram for the engine connections and one diagram for the instrumentation.

Click to expand...

Thank you, boscoe! That is help I was looking for. I will work on it tomorrow.

boscoe said:

The green wire from what Yamaha calls the "lighting" coil is used to provide the tachometer RPM signal. There are several connectors along the way from the lighting coil to the green wire that is in the ten pin harness. The connections in the ten pin connector as well. The connections from the control box to the tachometer. I would inspect all of those connections. Plus the wiring itself.

You can see these connection points in the Yamaha service manual. One diagram for the engine connections and one diagram for the instrumentation.

Click to expand...

I got to checking the wiring all the way back to the lighting coils. One benefit of having both engines is I have readings and connections to compare to.
I ended up at the coil itself. The lighting coil tests open for ohms. Is the only purpose of the lighting coil to run the tach? It doesn't look like too hard of a job to replace.

Brad

The main purpose of the lighting coil is to generate electricity to recharge a battery. Or to illuminate lights. Via a rectifier. Or on some motors to power devices on the motor.

If your lighting coil is open then I suspect that there is 0 voltage output on your rectifier.

boscoe said:

The main purpose of the lighting coil is to generate electricity to recharge a battery. Or to illuminate lights. Via a rectifier. Or on some motors to power devices on the motor.

If your lighting coil is open then I suspect that there is 0 voltage output on your rectifier.

Click to expand...

I assume, then, that all I need to do is replace the lighting coil and the tach should work? I have not used this boat yet as I purchased it after boating season last year. It is very possible it was not charging the battery, but the last owner hadn't used it for a year due to health issues.

It isn't important to solving the problem, but, is it correct to say that the one wire that runs to the tach is counting crankshaft rotations and the other two wires are running to the rectifier for charging/running lights? I just want to see if I understand this part of the system.

Brad

Two green wires from the lighting coil. Both to the rectifier. One of the green wires is jumpered to another green wire that connects to the ten pin harness. The green wire in the ten pin harness runs to the helm. It connects to another green wire that runs to the tachometer.

The lighting coil creates AC electricity. AC is converted to DC by the rectifier. The tachometer is measuring the cycles in the AC and converting it to RPM.

boscoe said:

Two green wires from the lighting coil. Both to the rectifier. One of the green wires is jumpered to another green wire that connects to the ten pin harness. The green wire in the ten pin harness runs to the helm. It connects to another green wire that runs to the tachometer.

The lighting coil creates AC electricity. AC is converted to DC by the rectifier. The tachometer is measuring the cycles in the AC and converting it to RPM.

Click to expand...

Thanks. It was kind of the way I was thinking. Thanks for the lesson. Guys like you are very much appreciated on sites like this.

Brad