Mercury 135 Tach Help!!!!

[steveg72]

Hi everyone!

I've got a 1992 Mercury 135 that is having issues with the Tach. It was intermittent, now mostly inop although it does come on occasionally. I've checked the wires and all look secure. The needle moves to zero when the key is switched on, it hovers around 300 when off. The switch on the back is set to 12 poles. I've use an ammeter and get around 12.6 with it off, 13.6 when it is running.

Any ideas? Where is the recitifier on this motor to check?

Thanks!

Steve

 

[Chris1956]

Re: Mercury 135 Tach Help!!!!

That motor likely has one or two voltage regulators, located on or near the cylinder heads. The grey wire is the tach sender wire. In the VR is bad, the tach could be affected. You can switch the wire from one of the VRs to the other. That may help isolate a bad VR.

 

[steveg72]

Re: Mercury 135 Tach Help!!!!

OK, tried that and it worked. I guess I need a new VR? What else can i do to verify the VR is bad and it was not some other problem? The connection with the tach wire to the 1st VR seemed like a good connection.

Where is a good lace to find a VR?

Thanks!

 

[Chris1956]

Re: Mercury 135 Tach Help!!!!

A lot of times the VR will have a burn mark on the board which is visible thru the potting material. Sometimes the second Merc VR will burn out shortly after the first VR. CDI Electronics sells them, but I would google the part number and shop by price.

 

[steveg72]

Re: Mercury 135 Tach Help!!!!

Thanks Chris. I ordered one from Iboats, they had about the best price and I wanted to contribute here. My boat does not have a volt meter, but when I would check it with mine it looked normal. I can't see anything on the board yet, but I haven't removed it either. I will wait until I get the new one and see how it looks. Funny thing, when the tach was working, it seemed to come on in a certain rpm range. I'm guessing it was just a voltage output range where the tach would actually work?

Thanks for your help! We've got a big trip planned and I want everything to go smoothly so I'm happy to have this tracked down.(I hope).

 

[steveg72]

Re: Mercury 135 Tach Help!!!!

As a follow up: I finally got home from a work trip and changed it. Very easy to do, and yes the old VR had a burn mark on it that I couldn't see until it came off. New VR is in and all is well, hope it last for awhile and doesn't blow right away.

 

[Chris1956]

Re: Mercury 135 Tach Help!!!!

Steve, Glad it worked out. Just so you know, the second OEM VR on my motor burned out a few days after I installed the first new one.....

 

[j_martin]

Re: Mercury 135 Tach Help!!!!

Common failure mode is overheated stator (yellow) connectors. I usually solder and insulate those connections. I can't for the life of me figure out how they think 10 amp connectors can carry 20 amps without overheating.

 

[steveg72]

Re: Mercury 135 Tach Help!!!!

OK thanks! I will keep an eye on them.

When you say you solder them, what exactly do you do? You just solder the connection themselves?

I switched the tach over to the older VR and will see how it goes.

Thanks!

 

[j_martin]

Re: Mercury 135 Tach Help!!!!

OK thanks! I will keep an eye on them.

When you say you solder them, what exactly do you do? You just solder the connection themselves?

I switched the tach over to the older VR and will see how it goes.

Thanks!

I cut the connectors off, clean, twist, and solder the conductors. Insulate with adhesive lined shrink tubing.

I run mine hard all the time, as I've rigged to charge all 3 batteries every time the engine is running. No problems in years since the soldering. Carried spares on the water before that.