Analog Tachometer for Smartcraft

Electrical and electronic topics for small boats
CactusEd
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Joined: Sun Jan 19, 2020 10:37 am

Analog Tachometer for Smartcraft

Postby CactusEd » Mon Feb 17, 2020 9:18 am

Hello. Certainly this is going backwards technologically given the digital Smartcraft and VesselView options, but how would I go about connecting an analog Mercury tach to my helm wiring? No tachometer at all currently.

I'm assuming either a harness from the purple connector, or a proper connection to two or more of the single pigtails is the solution. Much thanks in advance.

1980 15 Sport side console, 2016 Mercury 60 ELPT

rsz_1rsz_smartcraft.jpg
rsz_1rsz_smartcraft.jpg (64.71 KiB) Viewed 6537 times
1980 Sport 15 side console - 2016 Mercury 60 ELPT

jimh
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Re: Analog Tachometer for Smartcraft

Postby jimh » Mon Feb 17, 2020 9:31 am

An analog or conventional tachometer needs three connections: power, ground, and tachometer signal.

In marine outboard engine wiring, the conductors are usually identified by wire insulation color:

VIOLET = switched 12-Volt positive from ignition key switch in the RUN and START positions
BLACK or YELLOW = battery negative
GRAY = tachometer signal

While wire insulation color is a reasonably good indicator of the signal and voltage being carried on a conductor, you should never rely completely on wire insulation as an identifier. Locate an OEM wiring diagram to verify the voltages and signals. In some instances, conductors now carry printed labels that identify their function.

If the OEM intended that a conventional analogue tachometer could be used, there should be provisions for it in the engine wiring harness to the helm.

An article I wrote in REFERENCE provides more guidance on interpretation of marine wire insulation color and usual functions. See

Marine Wiring Color Codes
http://continuouswave.com/whaler/reference/wireColorCode.html

In the image seen above, I don't see any VIOLET or GRAY conductors. Hence I cannot offer a suggestion that involves the wiring shown.

jimh
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Re: Analog Tachometer for Smartcraft

Postby jimh » Mon Feb 17, 2020 9:38 am

CactusEd wrote:I'm assuming [the tachometer would be connected to]...a harness from the purple connector...


I doubt that the "purple connector" is a point of attachment for a tachometer. What is shown appears to me to be a network hub. The unused ports are probably capped with a terminator or a weather-seal plug. The reason there is a difference in color of the attached plugs is to differentiate them; some are just weather caps and some are terminators. Only other Smartcraft devices would be connected to the ports on the network hub.

Consult an OEM rigging guide for advice.

CactusEd
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Joined: Sun Jan 19, 2020 10:37 am

Re: Analog Tachometer for Smartcraft

Postby CactusEd » Mon Feb 17, 2020 1:00 pm

jimh wrote:
CactusEd wrote:I'm assuming [the tachometer would be connected to]...a harness from the purple connector...


I doubt that the "purple connector" is a point of attachment for a tachometer. What is shown appears to me to be a network hub. The unused ports are probably capped with a terminator or a weather-seal plug. The reason there is a difference in color of the attached plugs is to differentiate them; some are just weather caps and some are terminators. Only other Smartcraft devices would be connected to the ports on the network hub.

Consult an OEM rigging guide for advice.


First off, thanks for the reference to the wire coding (although it appears that Mercury may or may not have followed that convention). There is a Smartcraft harness past number (Analog Gauge Harness 84-892990T01) that appears to link from the purple 14 pin connector to an array of single terminals labeled for tach, trim, oil pressure, etc. There is also a Mercury "Analog Gauge Interface", and I have seen mentions of having to re-flash the engine's ECU to enable signals to be passed to traditional instruments. Solid information on the whole process is in short supply.

Your OEM rigging guide suggestion is valid as well. Will have to see if I can find one to refer to.
1980 Sport 15 side console - 2016 Mercury 60 ELPT

jimh
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Re: Analog Tachometer for Smartcraft

Postby jimh » Mon Feb 17, 2020 2:16 pm

I am sorry I couldn't be more helpful, but, as you mention, on-line information from the OEM (Mercury) seems hard to find and in short supply. And I don't own any modern Mercury FOURSTROKE engines, so I don't have first-hand experience with them.

It may be possible that in the particular engine you have, the engine electrical system does not generate a conventional tachometer signal. The "conventional" signal is usually a 12-Volt DC waveform whose frequency changes in proportion to engine speed. This signal was usually derived from the alternator stator that was being excited by magnets rotating at the crankshaft speed, or what sometimes was once called a magneto and now is more commonly know as a permanent magnet alternator. The tachometer signal was just a half-wave rectifier version of the alternator output.

In some four-stroke-power-cycle engines the under-flywheel stator and rotating magnets are not used for generating electrical power, and a belt-drive alternator (adapted for marine use) that requires an external power source (the battery it is trying to charge) to supply the initial electrical current to make a magnetic field. Deriving a tachometer signal from that type of non-permanent-magnet alternator is not generally done.

The tachometer signal in a modern four-stroke-power-cycle marine outboard engine may be coming from the engine's control unit (ECU) or engine management module (EMM), where it is internally generated by the ignition controller from the crankcase position sensor data.

Your speculation that some sort of intermediate electrical module may be needed to convert the modern engine tachometer signal to something compatible with legacy analogue tachometers may be correct. If you figure out the solution, please follow up to this thread. I am always interested in collecting good information on marine electronics solutions.

CactusEd
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Re: Analog Tachometer for Smartcraft

Postby CactusEd » Mon Feb 17, 2020 2:29 pm

Absent better direction, I may end up spending more on an analog solution that just ponying up for the Smartcraft display.

I will post as efforts come to fruition. Lots of other things to tinker with in the meantime.
1980 Sport 15 side console - 2016 Mercury 60 ELPT

jimh
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Re: Analog Tachometer for Smartcraft

Postby jimh » Wed Feb 19, 2020 11:41 am

Based on browsing some on-line sellers, the component you are showing in your illustration above is a

Mercury-Mercruiser 878492K14 Smartcraft 4-way Junction Box

The component you have referred to as "the purple connector" is not a connector. It is a weather cap. The purpose of the weather cap is to create a weather seal for the connector into which the weather cap is inserted. The weather cap is identified by its violet color marking. Two weather caps are usually provided in the 4-way junction box OEM part packaging.

The four ports of the 4-way junction box are all equivalent ports. The presence of the weather cap indicates the port associated with the weather cap is not in use.

The device shown in your illustration that connects to a port on the 4-way junction box with a yellow marking is a Mercury 859318T1 TERMINATOR. The purpose of a terminator is to provide the proper resistive termination to the data network backbone at an end of the network backbone.

The use of distinctive colors to identify the weather cap and the network terminator components is to aid in visual identification of those components for the network installer.

The cable from the engine connects to one port of the 4-way junction box. Due to the orientation of the junction box in the image, the color identification marking of one device plugged into one port cannot be seen. That port has either a weather cap or a terminator attached, as indicate by either a violet (weather cap) or yellow (terminator) color identification marking. My guess: it is another weather cap. The other terminator would be at the far end of the network in the engine.