Mercury 60-HP BIGFOOT Tachometer Stopped Working

Electrical and electronic topics for small boats
dbtfree15
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Joined: Mon Jun 27, 2022 12:00 pm

Mercury 60-HP BIGFOOT Tachometer Stopped Working

Postby dbtfree15 » Wed Jul 13, 2022 7:53 am

The tachometer on my boat with a Mercury 60-HP BIGFOOT engine no longer works.

[The onset of the failure of the tachometer to work was mentioned in another thread that was discussing the replacement of the voltage rectifier-regulator assembly. That topic has been separated to this thread so it can be discussed on its own.--Moderator]

When the engine ignition key switch is moved to RUN, the tachometer dial pointer goes to 0 or sometimes 1000.

When the engine is running, the tachometer dial point goes to the far right peg at 6,000.

I have read that tachometers can go bad when a voltage regulator goes bad.

Q1: Is there another cause of tachometer failure besides voltage regulator failure?

In the wiring diagram for my Mercury 60-HP BIGFOOT engine there is a [gray] wire labeled "TACH" from the voltage regulator. In the engine wiring harness there is no corresponding gray wire.

One [unconnected wire with VIOLET insulation] is near the starter motor, but that wire cannot reach [the gray wire at the regulator].

Another wire with [gray insulation with a white stripe] is capped off; that [gray with white stripe] wire that can reach [the gray wire on the voltage regulator]--but [the wire insulation colors ] are not the same.

For a moment I connected [the gray wire from the alternator to the gray with white wire in the engine harness], but the tachometer reading did not change.

Give me advice on how to get the tachometer to work.

jimh
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Re: Mercury 60-HP BIGFOOT Tachometer Stopped Working

Postby jimh » Wed Jul 13, 2022 8:07 am

dbtfree15 wrote:Q1: Is there another cause of tachometer failure besides voltage regulator failure?
The most reasonable interpretation of the conditions described in your narrative: the tachometer is not indicating engine speed because the tachometer signal is not connected to the tachometer gauge "S" terminal.

The usually wire insulation color that is used for a TACHOMETER SIGNAL is GRAY. The wire on the new rectifier-regulator assembly that is GRAY is most likely intended to be the tachometer signal. If this wire is not connected to the tachometer, it will be very likely that the tachometer will not work.

To determine how to route the tachometer signal to the tachometer, inspect the rear face of the tachometer gauge. Typically the tachometer will have terminal posts. The terminal post for the tachometer signal is usually indicated with the identifier "S". Locate the "S" terminal.

If the tachometer does not have separate wire posts and uses a multiple-pole connector, you will have to consult the wiring diagrams to determine which wire is the tachometer signal input. If the wire insulation colors are typical for an outboard engine, the tachometer signal will still be on a wire whose insulation is GRAY or some variant of GRAY.

Observe if there is a wire that is part of the engine wiring harness that is already connected to the "S" terminal on the rear face of the tachometer. If there is such a wire, then locate the other end of the wire at the engine end of the engine wire harness. This wire can be used to carry the tachometer signal to the tachometer from the rectifier-regulator.

Regarding the use of wire insulation of different colors to carry a particular element of an electrical circuit: the wire insulation color GRAY is generally used for the TACHOMETER SIGNAL

In marine wiring, the wire insulation may have a second color in a stripe. The second color generally indicates a modifier to the main color. The wire insulation color GRAY is also used to navigation lamp circuits. In the instance of a wire with insulation color GRAY with WHITE STRIPE, the general interpretation (and particularly on a Boston Whaler boat) would be that the wire is related to the navigation lamp for the ANCHOR LIGHT function. But if the wire is in the engine wiring harness, that seems unlikely. More likely the GRAY with WHITE is related to the tachometer. Check the engine documentation for more advice. Some general wire insulation color guidelines are given in the RERFERNCE article on that topic at

Marine Wiring Color Codes
https://continuouswave.com/whaler/refer ... rCode.html

The behavior described for the dial pointer of the tachometer to float between the 0 (zero) dial scale and the 1000 dial scale in the absence of a tachometer signal is probably indicative that the tachometer is working.

jimh
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Re: Mercury 60-HP BIGFOOT Tachometer Stopped Working

Postby jimh » Wed Jul 13, 2022 1:23 pm

Another thought: if the engine is a four-stroke-power-cycle engine and was refitted to the boat which had a two-stroke-power-cycle engine and the tachometer was original with the boat, then tachometer may not work with a four-stroke-power-cycle engine.

dbtfree15
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Joined: Mon Jun 27, 2022 12:00 pm

Re: Mercury 60-HP BIGFOOT Tachometer Stopped Working

Postby dbtfree15 » Sun Jul 17, 2022 10:11 am

I played around a bit with [several undescribed elements of the tachometer or the wiring or the engine] and got [the tachometer] working better--but not great.

[The tachometer] now seems to work somewhat realistically--except [the dial pointer] bottoms out at 500 (now even when the power is OFF) and tops off at 3000. I know [the Mercury 60-HP BIGFOOT engine] is running [at engine speeds greater] than [the 3000-RPM maximum indication on the tachometer].

[The engine speed indicated on the tachometer] seems to work proportionately until [the dial pointer reaches] about 3000. [The dial pointer] then just stops going upscale.

[I plan] to replace [the tachometer with a new tachometer] and see [if a new tachometer works properly]. I think [the cause of the faulty engine speed readings] is the tachometer itself.

[Substituted for the pronoun "it" in many places in order to improve the information content in searching. No one ever searches for "it".--Moderator]

jimh
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Re: Mercury 60-HP BIGFOOT Tachometer Stopped Working

Postby jimh » Sun Jul 17, 2022 12:54 pm

If the tachometer is now responding to changes in the engine speed by indicating an increase in engine speed, then you must have made some connection between the GRAY wire from the Rectifier/Regulator assembly and what I would expect would be a terminal on the back of the tachometer with the label "S".

Please comment further about what change you made to get the tachometer to respond to engine speed changes. This could be helpful for others with a similar problem.