tach for 1982 merc 115hp?

[115mirrocraft]

just purchased the 5 pin wiring harness for my quick silver control box. The tach I have only has a negative and positive terminal. I connected the purple wire to the + and the grey wire to the - terminal. I then attatched the black wire to the tach mounting bolt to ground itself. I am also jumping power to my fuel gauge from the tach, fuel gauge works and back light comes on. but when i turn the key tach needle jumps to 6000 and stays there. ran the boat in driveway tach moves a little bit but stays in 6000 range. there is also no adjustment screw on tach. it is the round dial type and is black probably original too boat which is a 1985 mirrocraft offshore gl 17'. Do I have the wrong tach or is it something else? any help greatly appreciated. tach also has light in back of it but is missing.

 

[Barnacle_Bill]

Re: tach for 1982 merc 115hp?

The black wire should go to the - (neg) terminal and the gray wire is the tach input.

 

[115mirrocraft]

Re: tach for 1982 merc 115hp?

Thank you. I would then be able to run the purple 12v wire to the gas gauge?

 

[1nebel0]

Re: tach for 1982 merc 115hp?

yes

 

[Chris1956]

Re: tach for 1982 merc 115hp?

Most tachs built after the mid 70s have three connections. the wiring colors are normally purple for +12VDC, black for ground and grey for tach signal. You need all of them connected.