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How do i hook up an external tach to a 86 johnson 88hp engine

J

jerryny

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I have a 1986 Johnson 88hp SPL engine. I want to hook up my automotive tach to watch the RPM's. Does anyone know where I would connect the clips. thanks in advanced.
 
The boat has a tach, its just not working. Where would Chappall hook up the tach to the Johnson 88HP SPL engine. Anyone have any ideas. Thanks in advance.
 
Unlikely you'll be able to have that automotive tach work on your outboard. OMC engines must use a tach that functions off of a charging system that provides 6 pulses. However, the following may be of interest to you.

If your present tach is hooked up, perhaps the tach is okay and the rectifier is bad... check the rectifier as follows.

(Small Rectifier Description & Location)
(J. Reeves)


On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.


The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:


One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.

Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
********************
(Small Rectifier Test)
(J. Reeves)


Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.


Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.


Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.


Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

-------------------------

If on the other hand, you know the tach is bad and the rectifier is okay...... Most tachometers have four wires, Red or Purple for the voltage lead, Black for ground, Blue for instrument light, and Gray for the tachometer sensor feed.

1 - There should be a Gray sensor lead wire protruding out for the instrument cable (engine to dash), if not the tach gray lead would connect to one of the rectifier's yellow leads, yellow/gray if it exists.

2 - Blue connects to the light switch.

3 - Black connects to any good known ground, BUT NOT either of the two "M" terminals of the ignition switch!

4 - Red or Purple (usually purple) connects to the "A" terminal of the ignition switch.
 
Last edited:
it looks like noone in here wants to touch this including me....but i have a question regarding the tach you have in the boat....or rather a related question...what does the voltmeter read when you are turning 2k rpm or better?
 
joereeves said:
Unlikely you'll be able to have that automotive tach work on your outboard. OMC engines must use a tach that functions off of a charging system that provides 6 pulses. However, the following may be of interest to you.

If your present tach is hooked up, perhaps the tach is okay and the rectifier is bad... check the rectifier as follows.

(Small Rectifier Description & Location)
(J. Reeves)


On most 2,3,4,6 cylinder engines, the small rectifier is located on the starboard (right) side of the engine just in front of the engines electrical wiring strip. There are a few older V4 engines that have the wiring strip on the rear portion of the engine and the rectifier would be located just under that terminal strip. The smaller horsepower engines usually have the rectifier located on the starboard side of the powerhead close to the carburetor area.


The rectifier appears to be a round object approximately one inch (1") in diameter and also about one inch (1") high. The base of it is sort of triangular in appearance and is attached to the engine with two (2) screws/bolts..... usually one screw/bolt is larger than the other. The rectifier, depending on which one your engine uses, will have either:


One Red wire, one Yellow wire, and one Yellow/Gray wire, or One Red wire, and two Yellow wires.

Note that either of the above rectifiers could have a fourth wire which would be Yellow/Blue

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay auction at:

http://shop.ebay.com/Joe_OMC32/m.html?_dmd=1&_ipg=50&_sop=12&_rdc=1
********************
(Small Rectifier Test)
(J. Reeves)


Remove the rectifier wires from the terminal block. Using a ohm meter, connect the black lead of the ohm meter to the rectifier base (ground), then one by one, connect the red lead of the ohm meter to the yellow, yellow/gray, then the red wire (some rectifiers may also have a fourth yellow/blue wire. If so connect to that also). Now, reverse the ohm meter leads and check those same wires again. You should get a reading in one direction, and none at all in the other direction.


Now, connect the black lead of the ohm meter to the red wire. One by one, connect the red lead of the ohm meter to the yellow, yellow/gray, and if present, the yellow/blue wire. Then reverse the leads, checking the wires again. Once more, you should get a reading in one direction and none in the other.


Note that the reading obtained from the red rectifier wire will be lower then what is obtained from the other wires.


Any deviation from the "Reading", "No Reading" as above indicates a faulty rectifier. Note that a rectifier will not tolerate reverse polarity. Simply touching the battery with the cables in the reverse order or hooking up a battery charger backwards will blow the diodes in the rectifier assy immediately.

-------------------------

If on the other hand, you know the tach is bad and the rectifier is okay...... Most tachometers have four wires, Red or Purple for the voltage lead, Black for ground, Blue for instrument light, and Gray for the tachometer sensor feed.

1 - There should be a Gray sensor lead wire protruding out for the instrument cable (engine to dash), if not the tach gray lead would connect to one of the rectifier's yellow leads, yellow/gray if it exists.

2 - Blue connects to the light switch.

3 - Black connects to any good known ground, BUT NOT either of the two "M" terminals of the ignition switch!

4 - Red or Purple (usually purple) connects to the "A" terminal of the ignition switch.
Click to expand...

Joe, the tach kinda of works. It gets stuck at whatever the max rpm you run at. It will go from 0 to 4500 but when you slow back down the tach stays at the whatever the last high RPM was. Turning the key off resets it back to 0. Sound like a flaky tach?? I will perform the tests you suggested. I always like learning new things. Thanks
 
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