Jumping Tachometer

Hey Haventaclue,

The old Mariner is doing great, but last evening while running down the lake, everytime I hit the trim button the tachometer would jump. Never done this before and all it running okay. Is this normal or should I do some electrical checking??

Dave

Good to hear it.Trim button in the control box shift handle? Probably a short/touching wires inside,but I would start back at the motor and work my way forward,easier to see bare wires,battery fully charged of course.Tach wire clean and tight on the rectifier?

Don't see any problems at the powerhead. Yes the trim button is in the contol handle, and I've never had one of them apart. Is this going to be "fun" or just somthing to take slow and easy? The only wire on the rectifier is a red wire, (other than the two yellow wires from the stator) I think the tach connects thru the control box, not sure which wire its picking up the pluse signal from) And yes the starting battery is new and fully charged. Alternator is working good, (shows between 14 - 16 volts at WOT).

There should be a gray wire on the rectifier,that's the tach signal,here's a link to a wiring diagram http://www.maxrules.com/oldmercs/Wiring/1966ona/37.jpg .You need to find the gray one and move it.Try that first.The control box is not difficult after a half dozen times,plenty of photos as you dismantle it and a good service and a bit of grease on it won't do any harm either.Be sure and let me know where you find the gray wire! Oh Mariner were just Mercs painted a different colour.Except the Yamaha built Mariners which were copies of the Yamaha's own older motors up to 60HP between '74-'92.See Graham I do pay attention in class

Okay, I'm blind, (50+ years), the gray wire is there. The one thing I do know is wiring, checked all connections at the power head, all clean and tight. Ohmed the wire out from power head to tach and all is well, all connections at the tach are clean and tight also. I have not looked into the control box, but doesn't the gray wire travel all the way through? I tried working the trim switch while the meter was connected (ohms) but didn't get any flucuations there.

I know the power trim is a heavy electical load under power, but with a fully charged battery and working alternator I wouldn't think it would effect the tach in anyway. (never has) I'm going to try running a new wire (temporary) from the recifier straight to the tachometer, and a clean ground striaght back, I'll let you know how it goes. This should eliminate any interference. If the problem is still there, will have to be in the tach itself or the stator in some way. As you know the stator is new.

There I go again trying to teach Granny to suck eggs.You are probably correct about the tach on the way out.I didn't think about that Is there three wires to the tach,gray = sig.,black -,and a +?

Yes there is, and I'm going to check the ground side really well. In most electrical circuits the ground is more often the culprit. I'll keep you informed.

I fixed the jumping tachometer needle, turned out to be the recifier, not sure why, but mechanic friend had one doing the same thing and thats what he found. Mine is new, but of course doesn't mean it's good, and it shows 15+ volts at WOT, but I had another on hand so I just tried it out and no more jumping needle, still shows 15+ volts at WOT, I can't explain it by hey, it's fixed.

Good stuff.Takes very little to wipe out a rectifier or maybe it was just a faulty one