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Tach doesn't work on 2003 Johnson 150

T

TerryMason

New member
I'm trying to help my dad troubleshoot his boat - It's never run right since he bought it about 3 years ago (he didn't test drive it before buying it..).


2003 Johnson J150PLSTM


The problems (in case some are interrelated):
1. The tach works only 20% of the time. The rest of the time it sits at 0.
2. Sometimes the engine lights on the tach show that the engine is overheating. This happens after idling for about 3-5 minutes. The engine won't run over 2500rpm during this.
3. Last time he took it out, he lost all electronics, and the motor wouldn't start.




I want to start with the easier stuff, and fix the tach first. I've begun by looking at all the connections, and they all look good, except for this one, on top of the engine. I believe it's the rectifier, but I'm not sure.

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I've unplugged the tach, and plugged it in again. While working on the tach, and checking connections on the engine, the tach started working again, and continued to work for 10 minutes or so. I put the covers back on the engine, and started it up, and the tach no longer worked. No amount of wire wiggling would make it start working again.


So, I'm stumped, where should I start to get this tach working again?
 
A connector itself burns only if a loose terminal or connection exists (arcing!). Fix that first as Boobie suggests, then if the tachometer still acts up, that would be due to a flawed voltage regulator/rectifier assembly explained as follows.

(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)

A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).

A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.

However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.

The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.

NOTE: For the later models that DO NOT incorporate a wiring terminal strip, splicing into the "Yellow Wire" mentioned will be necessary.


Normally the Gray wire leading from the tachometer is attached at the terminal strip to another Gray wire which leads from the water cooled voltage regulator/rectifier...... remove the gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.

If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.

I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.

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
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Thank both of you, I'll replace the connector first, as you suggest. I'm having a heck of a time finding a replacement / reading the diagrams. Can you tell if my problem connector (it plugs into the top of the power pack) is either 6 or 8 on this diagram, or something else entirely:

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