CONTINUOUSWAVE

[The tachometer associated with a 1996 Evinrude 70-HP engine is not working.] How do I rule out the tachometer itself?

What color wire and where is it attached on the motor?

Coil top, middle or bottom?

Bob

If you plan to perform diagnostic investigation and service work on your outboard engine, the most important tool to have is the factory service manual. Purchase of the factory service manual will make servicing problems and diagnosis of problem much easier.

To test the tachometer for a two-stroke-power-cycle engine for functionality, connect it to another two-stroke-power-cycle engine. Note that on a typical analogue dial-pointer tachometer, the resting position of the dial pointer won't be at the 0-mark on the scale.

Your question about coils seems to reflect of an error in your understanding of how the tachometer in a typical two-stroke-power-cycle outboard engine works. A two-stroke-power-cycle engine tachometer is not usually driven by a connection to an ignition spark coil. They typically connect to a half-wave rectifier tap in the alternator.

To learn what wire color insulation is used in Evinrude engines for various functions, see

Marine Wiring Color Codes, OMC Engine
http://continuouswave.com/whaler/reference/wireColorCode.html#OMC

To deduce where the tachometer is wired to in your rigging, follow the wiring on the rear of the tachometer. Typically an OMC tachometer has four terminal posts on the back. There will be two posts for power connection, one for the switched ignition power (I), usually a violet wire, one for ground (G), usually a black wire. One post is for a voltage for gauge illumination (L), usually a blue wire. The electrical signal from the engine is attached at post (S), and is usually a gray wire.

To discover where the wire goes that is attached to post (S), follow the wire in the wire harness back to the engine. In most OMC engines this wire connects to a lead from the RECTIFIER-REGULATOR assembly.

Because the signal for the tachometer is derived from a half-wave tap in the rectifier circuit, it is very common that a problem with the engine magneto charging circuit which has damaged the rectifier will cause the tachometer signal to become disturbed, causing the tachometer to stop working.

I have both the ENGINE and ACCESSORIES manuals. Looks like Section 8, "Electrical System" specifically 8-28.

What does this rectifier/regulator look like?

I have the non-gauge alert system.

Bob

Bob--I am certain the factory service manual has an illustration that shows the rectifier in the manual.

To see a drawing of components of almost any OMC engine made in the last 25 years, visit the website SHOP2.EVINRUDE.COM.

For your engine, select the category EVINRUDE. Select the year 1996. Select the horsepower 70. Select the model E70TLEDA 1996. Select the drawing IGNITION SYSTEM. Select the part with callout 63. You will see a drawing of the rectifier assembly.

Thanks again Jim. I thought [the rectifier assembly] might be [as shown above].

Before I start troubleshooting and break out the multimeter, it makes sense to first and foremost make sure that the connections at the tachometer, the terminal board, and rectifier-regulator are in working order, that is, lacking corrosive oxidation, and properly secured.

Part of the diagnosis requires running the engine at 1,000 RPM. How am I supposed to determine that if the tachometer is not working?

Bob

I suspect that the factory service manual diagnostic procedure calls for connecting a shop tachometer to the engine, or perhaps you can just estimate an engine speed of 1,000-RPM by ear.

The first thing I'd check is the continuity of the circuit from the engine to the tachometer.

Was the tachometer working before you performed some repairs on the red Amphenol connector in the engine wiring harness?

jimh wrote:Was the tachometer working before you performed some repairs on the red Amphenol connector in the engine wiring harness?

I do not know. The wire connection that I had to replace was for the fuse (red wire w/violet band). That connection is not as secure as the rest of the male connectors in the rubber of the Amphenol connector, and when I separated it to clean out the dielectric grease, it touched one of the other connectors causing the 20A fuse to blow. I saw the spark, then discovered I had nothing when turning the key to the "ON" position. Fuse replaced.

Bob

Generally nothing good happens when there is sparking of the 12-Volt circuit to ground. Before working on any electrical wiring, the electrical power to all the circuits should be shut off. Don't work on electrical connectors that are carrying live power.

jimh wrote:Before working on any electrical wiring, the electrical power to all the circuits should be shut off.

Beginners luck and I wasn't expecting that to happen. Law of unexpected consequences I guess. I will make sure the battery is disconnected in the future.

Bob