'73 Merc 115hp with Airguide Sea Speed Tach problem

bmbecker

Cadet
Joined
Mar 27, 2009
Messages
17
I have a '73 Merc that I am working on. I am attempting to get the timing and carbs set up and have this old tach that was on the old boat that this motor was on when I got it. It was hooked up but had some HORRIBLE water damage to the wiring and there was no way of tracing how it was hooked up. It only has 2 wires coming out of the back of it. One is lime green colored and the other is black. I would assume that the black is ground but I don't know were the green hooks to. Any one had this problem or know what I am talking about that might have some info for me...I would love to hear from you. Thanks for your time and help.

Tach is "Airguide- Sea Speed P-6487

Thanks!!
 

75TowerOfPower

Petty Officer 1st Class
Joined
Apr 17, 2009
Messages
331
Re: '73 Merc 115hp with Airguide Sea Speed Tach problem

The green will actually eventually hook up to the rectifier. It will read the pulses the stator puts out. It takes those pulses and turns them into rpms aka pulse per minute.

Normally the motor has a 7-8 pin output that will "plug" into the side of the motor and then on the inside it will continue. You can check to see if there is continuity between a wire coming of the rectifier and whats connected to the tach.
 

INDYCAVER1

Seaman
Joined
May 15, 2010
Messages
51
Re: '73 Merc 115hp with Airguide Sea Speed Tach problem

Hey, I know this is a old post, nut I had questions about the same tach. I have a 70 115 merc. I had this tach hooked up to a 72 85 hp Johnson and it worked fine, but I didn't know if it would work with my merc. On the front of the motor is says use only quicksilver tach. I'd love to keep the tach I have cause it matches my speedo, bit don't want to risk it getting fried or not working properly. And advice is great.
 
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