how to hook up a tach to johnson motor

[spacerust]

ok, so i just recently switched motors on my boat. i had a merc now i have johnson. the guy gave me a tach to put on but i had one on before. what do i need to do to get it going for the new motor. when i took her in the water the old tach wasn't working. but i don't recall unhooking anything related to the tach when taking the old motor off.

 

[emdsapmgr]

Re: how to hook up a tach to johnson motor

What model engine do you have?

 

[Silvertip]

Re: how to hook up a tach to johnson motor

I assume you changed the control box to Johnson/Evinrude. Look below the key -- you will find a three terminal plug. That's where the tach gets connected. You'll need the tach harness or make your own using terminals that you can get at Radio Shack.

 

[spacerust]

Re: how to hook up a tach to johnson motor

ok, no wires under the key. what do i need to do or buy from radio shack? also i have a speedometer too...could i hook this up as well? what do i need for this too. i just bought an owners manual from ebay but i really want to work on this in the afternoons. lol...i'm too impatient to wait for the manual to arrive.

thanks!

 

[spacerust]

Re: how to hook up a tach to johnson motor

i have a 1973 johnson 135hp.

 

[emdsapmgr]

Re: how to hook up a tach to johnson motor

The 73 johnsons do not have the 3-wire setup for the tach. You should find a cutoff grey wire coiled up inside the control box. This is the tach signal wire. Splice it and run it to the "S" terminal on the tach. You will also need to get postive and negative from your dash to run the tach. Any new speedo should come with 23' of hose and a pitot which will mount to the back of the boat. The speedo operates by water/air pressure through the hose.

 

[spacerust]

Re: how to hook up a tach to johnson motor

would you happen to have a diagram of what goes where? it's simple but is there any consequences if i hook it up wrong?

 

[phipps]

Re: how to hook up a tach to johnson motor

The 73 johnsons do not have the 3-wire setup for the tach. You should find a cutoff grey wire coiled up inside the control box. This is the tach signal wire. Splice it and run it to the "S" terminal on the tach. You will also need to get postive and negative from your dash to run the tach.

Would this also apply to a 71 Johnson? Would explain one of the extra wires inside my control box.

 

[ezeke]

Re: how to hook up a tach to johnson motor

Please click the thumbnail.

The normal wiring takes the tach positive voltage from the accessory post on the ignition switch (purple wire) and the negative (solid black wire) from the smaller M post on the ignition switch.

The light is generally wired to your light switch or to the light post on one of your other gauges using blue wire.

 

[phipps]

Re: how to hook up a tach to johnson motor

Thanks for the wiring diagram. Helps me a lot!

 

[fatboyntn]

Re: how to hook up a tach to johnson motor

Please click the thumbnail.

The normal wiring takes the tach positive voltage from the accessory post on the ignition switch (purple wire) and the negative (solid black wire) from the smaller M post on the ignition switch.

The light is generally wired to your light switch or to the light post on one of your other gauges using blue wire.

This is exactly the way I hooked up the tach on my '73 115 Evinrude. Works great. Also used the purple wire as the source of power for my temp gauge. When the motor is in the "off" position, the temp and tach gauges do not draw current and won't run the battery down. Just don't load it down too much. There is a small fuse that is located on the engine that can blow if you draw too much current.

 

[wwfranklin@comcast.net]

Re: how to hook up a tach to johnson motor

What model engine do you have?

I have a1997 50hp johnson

 

[emdsapmgr]

Re: how to hook up a tach to johnson motor

We've got two threads going at one time here. Franklin, you should note Silvertips's comment at the start of this thread. If your control box has a trim switch in the handle, there should be a 3-wire connector pigtail dangling from the handle of the control box.