Tachometer not working right

[brian62]

I have a 1989 70 hp mercury engine that the tach is not working. I bought a replacement tach same as the one I had before. I have power (battery) to the tach and the ground is grounded. The gray wire (Sender) gets signal when turning over the engine but the tach when cranked goes the oposite direction and when running the tach just sits there.

I have the setting the same as previously set at 4= Pole

I can't find a wiring diagram to verify if the power should go to a specific place. Ground is ground.

Any ideas how I can get this working right?

 

[Chris1956]

First of all, the tach is set to "4". It should be set to "6". Mercs generally uses the 12P or 6C settings, whichever you have.

Also, some tachs have a separate connection for nav lights. You have the +12VDC connected to the light. Is it possible that the other screw is for running the tach itself?

 

[Faztbullet]

It is wired correctly...Merc tach the light is always on when key/motor is on. Need to check rectifier

 

[brian62]

The rectifier is working correctly. I connected the replacement tach directly to the engines rectifier, power and ground, including different settings just to see if it worked. It appears the replacement tach is bad as well. Would what I did confirm my suspicions?

 

[jimmbo]

If 2 tachs aren't working, I suspect either both were fried by your Engine, or both weren't getting the correct Signal. You say the Rectifier is Good, then the Stator might be having an Issue

Just out of Curiosity... How long have you had this Motor?

 

[brian62]

If 2 tachs aren't working, I suspect either both were fried by your Engine, or both weren't getting the correct Signal. You say the Rectifier is Good, then the Stator might be having an Issue

Just out of Curiosity... How long have you had this Motor?

It's a 1987 engine.

 

[jimmbo]

It's a 1987 engine.

That's not what I asked