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95 Mercury 115 ELPTO Repeatedly Blowing Rectifier / Switch Box

S

Sierra Ranger

New member
Hi, hoping for some guidance. I'll try to keep it clear. I purchased a used non running 95 Ranger with a Merc 115 ELPTO 2 stroke outboard. It would not run well. The tach moved wildly. I found a cooked yellow wire on the rectifier, replaced the rectifier and found it ran better but not right. Replaced the switch box and the engine ran very well. The tach worked proper. Both were Amazon Chinese replacements. After about 2 hours on the water run time both units failed. Once again the tach went haywire. Being there is no mechanic within 40 miles that will work on 2 stroke outboards, after researching, I replaced the stator, trigger, rectifier and switch box. The first 3 are CDI US made parts. The switch box is Chinese (I ended with 2 from the first order). The engine now runs well but after about 1.5 hours the tach went haywire for only about 5-6 seconds at a low cruising speed of around 1800 RPMS. If I was not looking at it I could have missed it. I ran the engine for another hour with no issues (mixed RPM's, mixed starts and stops). I suspect there is still an unrepaired issue lurking.

Battery is a new correct marine flooded traditional unit, fully charged.

Connection is wing nut with starter leads on the bottom of the stack. Cables are clean. Will change to proper clamps.
Ran the CDI suggested test for the ignition key and found no shorts.
Inspected as much of the wiring in the engine as possible and found nothing afoul.

What would cause the tach to have intermittent wildness?
Dave
 
You have a 2+2 engine. It runs on 2 cylinders up to about 1800 rpms, then jumps to 4 cylinders above that. This may explain your tachometer observations at that rpm. I have two of them and Texas Mark has one as well, among others. What does that tach do above 1800 rpms? It should settle down unless you have something else going on.
 
The tach jumped to about 3000 rpm, then fell to about 1500, then up to about 2500 rpm then settled. Down. The engine sound didn't change nor did the speed increase or decrease. Its been rock solid at all RPM's otherwise for the 2 hours or so its been running.
 
Index the selector switch back and forth on the back of the tach to make sure it is correctly seated in the 12 pole alternator position. Make sure you gently push in on the switch with the screwdriver while doing this. Also look for any broken or loose connection on the purple, gray and black wires.
 
Get rid of the wing nuts and use proper lock nuts. Make sure all battery connections are shiny clean. Double check all the wiring plugs look for blackend terminals.
 
Yes planning on updating the wing nuts to proper locks. I certainly can check the tach. But my gut tells me there is a component somewhere that is grounding out or voltage is being dumped into the charging system? I dunno. Hoping the tach actions will help pinpoint where to look.
 
Now I'm thinking it might have something to do with the starting system. After the 1st repair the engine was running fine. It seemed as if it blew the switch box and rectifier right when it was started...or it was at shut down from the previous run. In other words, it did not fail while running. So there is a clue for someone out there with good electrical experience. Solenoid issue? The yellow wires from the voltage reg head down to 2 components along with the solenoid. I believe they daisy chain to each other but I'm not near the boat to post a pic. Can you tell me what those 2 devices are?
 
No connection between starting and running. Completely different systems. Disconnect the harness plug, wrap a rope around the flywheel, push down on the primer button if cold and pull it over, will start and run without a battery or starting circuit.
 
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