Install a tachometer and a speedometer 1979 402 40hp

[MacDaddy21]

I want to install a tachometer and a speedometer on my 1979 Mercury 402 40hp. It is an electric start with a control box. I know the control box has the little plug receptacle in the front for three wires. Not sure if that is the only hook up for a tach, and I'm not sure what kind of tach I can use.

As for a speedometer, I'd also like to get one of those hooked up. I don't really know what those take either or which one will work.

I've rebuilt and rewired nearly the entire motor, I just need some insight on how to do this, as it is new to me. Thanks.

 

[hotrod53]

Re: Install a tachometer and a speedometer 1979 402 40hp

The plug on the control box is for the tach, you need a short little wiring harness to hook it up. As far as a speedo, I have seen the ones that connect to the motor, there is a little hole on the leading edge of your lower unit that has a tube that goes up into the power head. Otherwise, you can mount one of those paddle wheel gizmos on the bottom edge of the transom that feeds back to your fish finder or a dash gauge.

The tach is probably the most important, that indicated a lot of how your motor is running. If you're just curious about how fast you're going, grab the GPS out of your car and read it.

 

[MacDaddy21]

Re: Install a tachometer and a speedometer 1979 402 40hp

Will any marine tach work?

 

[hotrod53]

Re: Install a tachometer and a speedometer 1979 402 40hp

I would have to so no, I think they are different for different types of ignition even thruout the same manufacturer. For instance I think one that works on a thunderbolt is different than a non-thunderbolt.

 

[dlplost]

Re: Install a tachometer and a speedometer 1979 402 40hp

Tach runs off of the alternator/generator (stator)coil. connects to one of the coil leads at the rectifier. Thats the tach signal at the connector at the front of the control box. Most aftermarket tach's have a switch in the back to select how many poles (pulses per revolution) on the charging coil. almost any tach with the switch on the back should work.

 

[MacDaddy21]

Re: Install a tachometer and a speedometer 1979 402 40hp

dlplost, thanks for the info. I'll see if I can find any information on compatibility between tach's and outboard models.

Just found this on ebay. Think it'll work?

http://cgi.ebay.com/ebaymotors/Hour...tQ5fPartsQ5fAccessoriesQ5fGear#ht_2082wt_1167

 

[BatDaddy1887]

Re: Install a tachometer and a speedometer 1979 402 40hp

....most people here would agree that boat speedos are a waste as you get more accurate readings with a GPS...even a car GPS will work. If you already have one on your dash and just want it to work, then go with hotrods suggestion. I would not drill a new hole in my dash for a speedo that is terribly inaccurate.

 

[MacDaddy21]

Re: Install a tachometer and a speedometer 1979 402 40hp

BatDaddy1887, like the handle, you and I got it figured out. And I am starting to see that you are correct with the speedometer inaccuracy. Id really rather just get the tach so I know how the motor is operating. I'm just curious now if the one I found on ebay would work. It says you are supposed to wrap one wire around the spark plug. Something about that seems really strange to me. Any ideas?

 

[BatDaddy1887]

Re: Install a tachometer and a speedometer 1979 402 40hp

MacDaddy....I got mine off Ebay and has worked for years! When you install your new/used tach, your engine calls for pole switch setting number 6P (pulses) on the back of the tach. Please don't wrap any wires around any spark plugs....all the power comes from the engine (grey wire) and come to think of it, I have only heard about that practice on motorcycles....of which I have never owned. Let us know how it all goes 'cause we like to see positive results!

 

[MacDaddy21]

Re: Install a tachometer and a speedometer 1979 402 40hp

Definitely will do, might be awhile before I get around to ordering one. Which one do you have?

 

[BatDaddy1887]

Re: Install a tachometer and a speedometer 1979 402 40hp

....I can't recall which one I have.....I know it's not a high-end one like a Faria....

 

[dlplost]

Re: Install a tachometer and a speedometer 1979 402 40hp

yes that will work, BUT...I'd go with a standard marine tach that reads off of the stator.

Look at this one...Ebay #220824375256
Look at the picture of the back of it. The switch lets it work on almost any motor. The 6P should read correct with yours I think.

And I too would skip the speedo, you don't really need it.

 

[MacDaddy21]

Re: Install a tachometer and a speedometer 1979 402 40hp

dlplost, thanks for the information. You are correct about the 6P setting. I found a site through mercury that has a chart that tells which
tach is required for each hp class, and 6P is spot on for my motor. Thanks!