Hooking a Tach up to a 3 Cyl Mercury 80 HP

JGra

Petty Officer 1st Class
Joined
Apr 24, 2009
Messages
222
I picked up a set of gauges for my boat today at a great price. The person that had them really did not know any history on them other then they were run on an outboard before. For 10 bucks it is worth a chance. The only question I have is on the tachometer. The gauges say US marine on the front and Faria on the back. In trying to look the tach up (6000 RPM) all I see for a 6000 rpm tach is for in I/O. There site says that the 7000 RPM tachs are for the outboards. This appears to be an older tach. The only markings is a sticker that give the switch settings. I can only make out the last 2 choices setting 3 for 12 pole, setting 4 for 20 pole. I cant make out the first 2. It only gives 4 choices but the knob goes to six. My question is will this work on my mercury 80 hp 3 cyl. I was told my eng was a 12 pole setup. The ony other markings is a stamp that says CS245F. Thanks
 

emckelvy

Commander
Joined
Jan 16, 2004
Messages
2,506
Re: Hooking a Tach up to a 3 Cyl Mercury 80 HP

You do have a 12-pole alternator on your motor. So if you set your tach to the 12-pole setting and connect the tach pulse signal wire to either one of the yellow wires coming off the rectifier, your tach should function.

Note that some of these 3-cyl's had a tachometer connection point between the stator windings and rectifier or rectifier/regulator. If you have a rectifier/regulator assy you may have one of these which does sorta look like the old-style rectifier. So you'd attach the tach lead to that block.

If you have just a rectifier, it's a square, smallish assy with 3 wires connected, red for batt+ and yellow wires to the other 2 terminals. In that case, the tach lead connects directly to either of the yellow wires.

If you have a standard Merc control box, you may be able to pick up a tach signal right of of a pigtail (or connector plug) coming out of the box. So check that out, that'd be the easiest connection point and would avoid having to run extra wiring back to the motor.

HTH.........ed
 

JGra

Petty Officer 1st Class
Joined
Apr 24, 2009
Messages
222
Re: Hooking a Tach up to a 3 Cyl Mercury 80 HP

Thanks Ed, This is a 1989 model. I do have a pigtail on my control. The wire colors are purple,grey,black,brown/white,tan.
 

JGra

Petty Officer 1st Class
Joined
Apr 24, 2009
Messages
222
Re: Hooking a Tach up to a 3 Cyl Mercury 80 HP

Hooked everything up and set the tach to 12 pole. Cranked her up and she idles by the tach at 700 RMP. Brought the fast idle up a little and everything seemed to work ok.
 

JGra

Petty Officer 1st Class
Joined
Apr 24, 2009
Messages
222
Re: Hooking a Tach up to a 3 Cyl Mercury 80 HP

Hooked up the Tach today and set it to 12 pole. Cranked her up and by the tach she was idleing at about 700 RPM's. Brought up the fast idle some and it seems to be responding ok. Thanks for the help.
 

Silver Eagle

Master Chief Petty Officer
Joined
Mar 16, 2010
Messages
852
Re: Hooking a Tach up to a 3 Cyl Mercury 80 HP

I have a 90 hp Mercury out board motor with oil injection. The boat is a starcraft pontoon boat (IT'S AN 07). My problem is my old tach died. I ordered a new one and After I put it on and put the boat in the water it doesn't work either. The tach is made for Starcraft. It doesn't have the four wires going to the back of the tach,it has a single slide one with a plastic clip on the bottom to lock it in place. I called a Starcraft dealer and they said to look at the motor for the problem,He didn't say what to look for. So what I need to know is what do I need to look for, I had the carbs worked on this year could they have loosened up some wire or cable ?What do I look for. There is no fuse box.
 
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