Logo
FULL SITE MENU

Help with Wacky Tach

A

asautt

New member
I installed a new tach and tri

I installed a new tach and trim gauge on my 91 Johnson 70hp. Had some trouble with broken connectors in the control unit plug for the tach harness. I ended up hardwiring the tach harness inside the control unit. Verified proper wire connections several times.

Trim gauge works fine. Set the tach for 6 poles. When I got out on the water the tach seemed to work when I first started the motor. Don't know how accurate it was reading but it seemed to track linearly up to about 3500-4000 rpm then took a huge leap and was bouncing all over the place. I think it even spun all the way around. Tried different pole settings with no improvement.

Besides the possibility of getting a bad tach is there anything else that could cause this? Bad ground? Rectifier going bad? Anything?

Thanks
Alan
 
"Tach should have a dial on th

"Tach should have a dial on the back of it. Set it to #6. It operates off of the 6 pulses that the alternating system emits.

If that engine has a water cooled regulator/rectifier.......

(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.

Remove that 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 store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store"
 
Thanks Joe.

I don't hav

Thanks Joe.

I don't have the water cooled regulator. Just the plain old can rectifier.

I will try hooking up the tach close to motor connecting at the rectifier. This would eliminate any capacitance or cross-talk in the wiring to the control unit and instrument panel.

Alan
 
Back
Top