Old tach with only 2 wires?

[DMAN1968]

Hello all,

I recently put a 1974 Johnson 115 onto my 1986 pontoon boat. The harness and cables all matched up and it is running like a top. I wanted to put the original old tach on the toon as well. When I took it out of the donor boat there are only 2 wires that run to the back of it...the sender wire and the ground wire (there is a wire for the light as well). Everything I have found on the forum says grey for sender, black for ground and purple for the power wire. Where does this tach get its power from? I thought maybe from the light but it wasn't on on the old boat all the time.

Also, the tach has a setting switch that only goes up to 4...anyone know for sure what that should be set on?

Thanks in advance.

 

[ezeke]

Re: Old tach with only 2 wires?

More description of the tachometer would help.

What colors are the two wires?

Are there any numbers, symbols, or names on the tachometer? Look inside the glass on the edge of the the printed surface for codes.

What is the top RPM shown?

 

[wilde1j]

Re: Old tach with only 2 wires?

Purple is a switched +12VDC from the ignition switch. Only powered when the sw is "on".

 

[ezeke]

Re: Old tach with only 2 wires?

A lot of old Airguide Tachometers only had two wires; the black one went to the engine ground and the other to the gray and yellow on the terminal block on most of them.

That's Airguide, though, there are many tachs over the last 34 years.

 

[DMAN1968]

Re: Old tach with only 2 wires?

Sorry about that I should have been more specific. I think it is original OMC for the time. There are no wires coming off the back of it, just 2 posts that are actually used to hold it in the console and then the wires form the engine are attached to those 2 posts. One is labled GRD and one SND. Then there is the grey wire that comes directly out of the light bulb socket. Top RPM is 6000.

Hope that helps. Thanks.