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Author Topic:   Adding Ammeter, Removing TRIM Gauge
Sea Gull posted 06-16-2014 09:38 AM ET (US)   Profile for Sea Gull   Send Email to Sea Gull  
I have a 1988 Boston Whaler Montauk 17 with a 1998 Johnson 115-HP outboard engine. I would like to eliminate the TRIM gauge on the console and replace it with an Ammeter. The rear of the TRIM gauge has a number of wires on it. I am hoping someone out there has done this modification. Any information on the procedure would be a great help and suggestions are welcome. Was looking for some wiring info for the tilt-trim gauge and a pick-up location for the Ammeter. What I am trying to obtain is a way to see and make sure that the engine is putting out enough power to keep my battery charged and run my electronics. Thanks
Chuck Tribolet posted 06-16-2014 01:27 PM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
An ammeter would need to be installed between the alternator
and the battery. That would get "interesting" with the
battery in the console. The ammeter would need to be able to
handle starting current, and they are aren't.

A voltmeter will do the job. If you've got voltage, and the
battery is good, the battery will charge. I replaced the
factory analog voltmeter with a digital unit someone here
recommended. That was plug and play. No, I don't remember
who made it, and the boat is 40 miles away.


DVollrath posted 06-16-2014 04:42 PM ET (US)     Profile for DVollrath  Send Email to DVollrath     
Sea Gull-- Ammeters that can handle starting currents do exist. They consist of a shunt and a voltmeter that is calibrated for that shunt's resistance. Examples include:

Look closely at the shunt's continuous and intermittent duty ratings to make sure it fits with your motor and dc load requirements.

The voltmeter that is measuring the drop across the shunt can typically be located a moderate distance away from the shunt. It is a fairly high impedance device (50 ohms for analog meter), and there is proportionally very little voltage drop in the leads, almost all is across the meter.

As an example, using the Blue Sea Systems 100A Analog shunt and the 100A analog meter, and running 24AWG 15' back to the stern from the console would have a drop of 1.5% across the leads, or a 1.5A error at full 100A scale.

My math is always deserving of a check or two...


Sea Gull posted 06-16-2014 06:01 PM ET (US)     Profile for Sea Gull  Send Email to Sea Gull     
Dennis- Thanks for the electronic class. It was my error on the post. I meant Voltmeter. When I remove the trim gauge, do I just cap off the wires and forget about them? Or, is there something else I should do with them? Where is the best point to hook into the positive side of the battery circuit for the Voltmeter? I had hopes of finding a wiring diagram of the tilt-trim wires before I start the change over.
Where can I search for that?
At this point I have more questions than answers.
jimh posted 06-17-2014 09:36 AM ET (US)     Profile for jimh  Send Email to jimh     
To learn more about how the TRIM gauge circuit operates, see

Mystery of the Trim Gauge


E-TEC Rigging: TRIM Gauge

The above articles contain detailed explanations of how the TRIM gauge circuit operates. Now that you are about to remove it, you can become more familiar with how it will no longer work on your boat.

When you disconnect the TRIM gauge, you can just insulate the wiring and set it aside.

To connect a Voltmeter, you could use the VIOLET conductor from the TRIM gauge wiring as the positive and the BLACK conductor from the other gauge's wiring as the negative.

Also, in many installations of conventional gauges the VIOLET and the BLACK circuits are daisy-chained from gauge to gauge. If you remove one of the gauges where the terminal posts of that gauge were being used as a common point in the VIOLET and the BLACK circuit, you will--of course you probably know this if you understand electrical wiring--have to maintain those circuits to the other gauges.

Sea Gull posted 06-25-2014 09:53 PM ET (US)     Profile for Sea Gull  Send Email to Sea Gull     
Did the change over and every thing went smoothly. Thanks for the input guys. It is nice to know that there are people out there that will help out other boaters. Thanks again for your help-
Sea Gull

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