1973 mercury 85 tach pole setting

[ljraffray]

I am trying to install a tach for my 1973 mercury 85hp motor. After connection, I started the motor and it jumped to 0 but would not go any further. It has the three (3) wires that come from the throttle and I followed the diagram and wired it accordingly. It was pre-set for #5 pole setting, is this correct?

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

probably should be set for '6' or '4'pending on serial number<br />-even if you're out on this setting, the tach should still register something. I think you should tell us how you wired it. Also, some old mercs used an ignition tach. What make, brand and style do you have?<br />

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

Wire colors are white, brown and black that come from the "MerControl" (throttle). I'm not sure exactly where they go but I tried it all ways until I turned on my ignition key and it went to "0".

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

If you tried all ways............it could be a problem..............tach could 'now' be fried.(or even worse...the control module if a ignition tach) I'll check to see if I have a pin out for the Control box plug.

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

brown = tach signal<br />white = positive <br />black = ground<br /><br />-don't inter-mix them, as you can damage the electronics in the tach(pending on the model)<br />-if she still don't work when wired right, test for 12v between the black and white with key on. Then check with an a/c voltmeter to see if you have voltage from brown to black when engine running. If you have these, and it still don't work, the tach is fried.<br /><br />-are you sure this is the right tach!!!!!!

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

I'll bet that the tach you have is for an alternator application, and even though my manual doesn't go back that far, I'll bet the wiring harness is wired for an ignition tach. I see no reason why you couldn't rewire the harness to fit an alternator tach.(presuming you didn't burn something already) What kind of tach is it??????????????<br /><br />

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

Thank you for the info. I am going deer hunting tomorrow evening and will not get to try this until Sunday...<br />Again, thank you so much.<br />I need to completly wire my boat. It doesn't even have lights or any gauges. Do you any schematics that might help with this major task?

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

It is a Faria marine tach (alternator). I couldn't even tell you if my motor has an alternator or not. Just got the boat on Tuesday.

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

I don't have an exact schematic, and since my plate is a little full lately(wife is on my case).........you might want to keep an eye on this posting, as most will apply to your boat as well. Its not done yet, as we haven't got gauges yet. Good luck hunting. I got a 5 point last weekend and hope to go out tomorrow if I can shake this flue.....<br /><br />

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

Odds are good it has an alternator under the flywheel. But I'll bet the brown wire is hooked up for an ignition tach. If you want to use this tach, you'll have to do some rewiring. (can you return this tach and get the recommended one?)

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

Don't think it's possible because it's electronic and I already connected/used it. They are very funny about these things.<br />What are your thoughts on re-wiring?

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

I'd do it in a flash. If you can't take it back, what do you have to lose? I'll help as much as I can, but I want you to trace that brown wire and tell me where it ends up.

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

I just got in from hunting.... did not see anything I was looking for! Had a major problem with two domesticated dogs running around and barking at me and my daughter will trying to sit very still and quiet. A real drag but next time we will have to do something about those dogs! <br /><br />I called the manufactor of the tach and they said the the ignition that I have (Thunderbolt ignition) will not work with their product. Needless to say, I WAS ABLE to return the tach for a refund. The same day I called a different manufactor and asked all the questions before purchasing another tach. The gentlemen told me that it will work but that I needed to cut the gray wire from my distributor and connect it to the rectifier. My question is, am I to run that gray cut wire:<br /><br />FROM THE DIST. TO THE RECT.<br />or<br />FROM SOMETHING ELSE (???) TO THE RECT.<br /><br />Any info will be very appreciated.

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

This is too funny...LOL. The second tach is the same as the first and requires us to rewire as previously described!!!<br />But you are ahead because you may have fried the first tach, and now have a new one to play with....<br />>isn't the signal wire at the control box "brown"? If it is, please trace it and tell me where it goes. (I suspect the switch box on engine)

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

I traced the wire from the throttle to the engine. It connects on side of a rectangular box in the front of the engine and then from the other side it goes to the distributor.

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

LJ!!good....<br />disconnect the brown wire from the box, (leaving all other wires intact) and reinstall screw. <br />>you should now have the brown wire loose.<br />>we want to connect this brown wire to the a/c side of the rectifier. Do you know where the rectifier is? Just to be sure, you better describe it to me to prove you do:<br /> >how many wires to it?<br /> >do two of them go under flywheel?

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

Not sure but.....<br />Is it about two inches square and has three wires connected to it. Two go under the flywheel and the other goes to the same rectangular box I mentioned before.<br />My need for understanding is I'm not sure which side of the brown wire to disconnect and re-route to the rectifier.

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

>the brown wire that comes from the throttle is to be disconnected from the box on the engine.<br />>It then should be reconnected to rectifier. It should be connected to one of the wires coming from the flywheel (doesn't matter which one) If you want I'll draw a diagram...

 

[ljraffray]

Re: 1973 mercury 85 tach pole setting

WE HAVE RPM'S!!!!!! <br />Connected the wire, cranked the motor and there it was... the smile on my face was priceless! It idles at about 1150 RPM (OK?).<br />Another thing I noticed was that the two wires from rectifier where filled with corrosion (not bad or very bad?).<br />Thank you for your great counsel schematic!<br />Me next project will be more gauges, swithes and lights.<br />My wife is just about out of grace with me tonight!

 

[petryshyn]

Re: 1973 mercury 85 tach pole setting

Yo..<br />All corrosion is bad. clean as good as possible and if still looks ratty, replace.<br /><br />One more thing to contend with. There is a selector on the tach for the number of poles on your engines stator. If its set wrong, rpm will be inaccurate. I beleive yours should be set at '6' as it is a 12 pole.<br /><br />Good fishin and good luck!!<br />