Installing a tach on a 79 90hp Mercury

[elr]

I would like to have a tach for my inline six. There is a round plug on the front side of the shifter-thingie (whatever it's called). Does that mean I can hook into there? How can I test it at the plug to make sure it will work before I buy a tach?

 

[Gomer50]

Re: Installing a tach on a 79 90hp Mercury

The plug on the remote control box consists of three wires 1=brown (sending wire that goes to one of the posts on the recitifier that go to the stator) 2= white wire 12volts and 3 wire black for ground.Make sure you purchase a 12 pole // 6 pulse marine tach. Auto tach wont work.

 

[elr]

Re: Installing a tach on a 79 90hp Mercury

So I can test the ground wire and 12-volt wire. Is there a way to test the brown sending wire? When you rev the boat up should the voltage increase on that wire?

 

[Texasmark]

Re: Installing a tach on a 79 90hp Mercury

The signal may be too narrow for a regular DMM to read. A "True RMS" Voltmeter may read it and being true RMS the value will go up as the frequency of hits increases even though the amplitude will remain relatively constant. So yes you should be able to measure it.....but I never did.

Mark

 

[elr]

Re: Installing a tach on a 79 90hp Mercury

I don't think I have any wire coming off the rectifier going to the tach. I only have three wires at the rectifier. Two yellow coming from the stator, and one I forget what color going to the battery, I presume. Does that mean I'll need to run a new one from the rectifier to the tach?

 

[Gomer50]

Re: Installing a tach on a 79 90hp Mercury

Take a look at your wire harness inside your motor and see where the brown wire goes it might be hooked up to your switchbox on the side that has green,red,white,black and brown.I am assuming this is still a distributor model.If it is take it off and hook it up to one of the yellow wires on the recitifier.

 

[elr]

Re: Installing a tach on a 79 90hp Mercury

I found a brown wire back at the engine that wasn't connected to anything. So I hooked it up to one of the yellow wires coming from the stator. And it is the same brown wire up at the plug. Both the black and white wires checked out ok too, so I should be good to go. Thanks for your help. Does anyone have any suggestions for a nice, quick, easy, good way to avoid paying $50 for a harness that plugs into my tach plug at the control box?

Thanks

 

[Gomer50]

Re: Installing a tach on a 79 90hp Mercury

I used a 3 phase green piece of extension cord with 3 spade connectors.with a spark plug wire boot that goes on a distributor. Real cheap.

 

[chum1]

Re: Installing a tach on a 79 90hp Mercury

Here ya go: install this thing to verify correct prop/ engine rpm adjustments then remove it and forget about it until you think you need it again.



http://cgi.ebay.com/Improved-Tiny-T...807?pt=LH_DefaultDomain_0&hash=item2a1306dedf

or

http://www.amazon.com/TINY-TACH-MODEL-TT2A/dp/B0045L9GA0

 

[elr]

Re: Installing a tach on a 79 90hp Mercury

Thank you, gomer50. Something like that is exactly what I'm looking for.

Chum1, I'll have to think about the tiny tach. I think I would like to have a permanant guage in the dash, just because. But we'll see. They look like they would be about the same price.