Hooking a tach to a 1979 merc 40 horsepower???

Maddoxsdaddy

Maddoxsdaddy

Petty Officer 1st Class
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Sep 22, 2008
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I'm trying to hook a teleflex tach to the controls of my 1979 merc 40. I bought the wiring harness so everything would be a direct plug in. Unfortunately for me, the send wire in the control box hook up is not putting out any voltage. I checked ignition and ground with a meter... they are ok. Before i go cutting into wires in the wiring harness from the motor to the control box to check voltages, can anyone tell me which wire is the send wire that i need to hook up to the tach?

Thanks in advance.
T.B
 
L

Laddies

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12,218
Re: Hooking a tach to a 1979 merc 40 horsepower???

Go back to the engine and make sure the sender wire is hooked to one of the yellow terminals at the rectifier if they a hooked there, then move it to the other yellow as a shorted diode will keep the tack from working.
 
Maddoxsdaddy

Maddoxsdaddy

Petty Officer 1st Class
Joined
Sep 22, 2008
Messages
222
Re: Hooking a tach to a 1979 merc 40 horsepower???

Great.... i'll check it out when i get home from work this evening. Does it matter which yellow wire i check or just switch them around and see if it works???
Thanks,
TB
 
L

Laddies

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12,218
Re: Hooking a tach to a 1979 merc 40 horsepower???

Your really not checking the wire if you have a OHM meter with the wires unhooked hook it yellow to yellow an if it's got continuity the stator will work, by swappinf the wires on the rectifier your seeing if one side of the rectifier is shorted out if you want a rectifier test we can send one.
 
Maddoxsdaddy

Maddoxsdaddy

Petty Officer 1st Class
Joined
Sep 22, 2008
Messages
222
Re: Hooking a tach to a 1979 merc 40 horsepower???

A recitifier test would be great. I checked voltage on the yellow wires and the red wire while the motor was running... the readings were all over the place... no steady voltage.
 
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