2 wire tach on 1978 Johnson 115

[klvn8r]

klvn8r
Cadet

• Join Date: Jun 2016
• Posts: 2

#1
[h=2]Tach hookup..78 Johnson 115[/h] June 22nd, 2016, 04:22 PM



Hi, new to this forum, and working on Dad's old Glastron. He has a two wire tach..one is obviously a ground not sure where to plug in the other. Engine has a CDI on it....which is the trigger wire? I tried to attach a pic, but was unsuccessful. I noticed that t one time, there was a ground wire from the throttle handle "box" and this is where the tach wire WAS running. I think a previous 'worker' cut the tach wire, and made it a ground for the control box. Sounds weird, I know. Is there a tach trigger in the tilt/trim electrical box, or does it go straight to the CDI, or elsewhere? Thanks!!!

klvn8r

 

[F_R]

Without knowing what "two wire" tach you have, it is impossible to answer the question. But a partial answer is the signal wire is grey and ground is to the box. The tach gets its signal from the AC sine wave from the alternator (grey wire).

Your tach may not be compatible. Has it ever worked on this motor before?

 

[rob 135]

2 wire tachs need a conversion box mounted on back of tach .

 

[klvn8r]

Thanks for the replies. It is a 2 wire tach, AT LEAST 20 years old. It was installed on the boat when the engine went on. As I recall, it worked for years, but the boat has been setting up the last few, and a boat shop had done some engine work....dad was not impressed. I looked, and there is no brand name on the tach. Any guesses? I'd post a pic if I could...

 

[F_R]

rob is suggesting it is an Airguide, which does need an amplifier. That might be true, considering its age. But if that is what you do have, I don't think it is compatible with today's systems.

 

[klvn8r]

I took a pic, but can't shrink it small enough....fwiw--the bezel looks like the OEM speedo, which is an Airguide. In tiny letters, there is AQUAMETER at the very bottom.

 

[klvn8r]

Just checked, selector switch on 6. I'm fairly sure this ran in the past...but someone snipped the wire running the length of the boat....does it go to the CDI or something in the tilt/trim box mounted on the transom? I do not have any "box" on the rear of the tach.

 

[F_R]

It has a selector switch?? That's interesting. Sounds like it is compatible after all. 6 would be the number of pulses from the alternator with each revolution. It gets those pulses from one of the yellow wires going to the rectifier. But it should not be necessary to run a wire all the way back there. There should be a grey wire in the remote control. That goes back to the rectifier, so just connect to it. Other wire is ground. I suspect it makes no difference which is which. The tach will always be "on". Not really, it only receives power from the alternator when the alternator is rotating (motor running).

 

[klvn8r]

The "remote control" you reference.....is that the little black box mounted back near the transom? Has the hot cables and tilt/trim wiring?

 

[Gary H NC]

The "remote control" you reference.....is that the little black box mounted back near the transom? Has the hot cables and tilt/trim wiring?

No,It is the box with your throttle and ignition at the drivers seat.

 

[klvn8r]

OOOOoooooohhh!!!! Now that explains why the tach wire that has been in the boat for all these years is so short. It will reach the t throttle box. Its all adding up now....should be able to get that done easily. Thank you, sir!!