1979 Mercury 80 HP Tach issues

K

Kissdude

Petty Officer 3rd Class
Joined
Sep 7, 2024
Messages
98
I was wondering if someone could please tell me, How do I connect a tach into my system?
I recently swapped motors from another boat that has a tach, my boat does not have one so I've taken the tach out of that boat and put it in my boat. The tach was used in the boat that I swapped from so it should work and I believe that it was working on the other boat. I have tried to hook it up but can't get it working, any idea what I have done wrong? Thanks!
 
C

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
28,237
Mercury tachometers need +12VDC, ground and stator pulses to operate. Normally a MerControl will offer these via plug on the MerControl or via pigtails on the newer Mercury controls.

The stator pulse is on either of the yellow wires that go to the rectifier. One of these should connect to a grey wire or perhaps a brown wire. A 1979 motor is about the time the wiring colors changed, so look at the choke solenoid. If that wire is grey, the pulse to the tach will be brown. If the choke solenoid wire is yellow/black, then the stator pulse to the tach should be grey.
 
K

Kissdude

Petty Officer 3rd Class
Joined
Sep 7, 2024
Messages
98
Chris1956 said:
Mercury tachometers need +12VDC, ground and stator pulses to operate. Normally a MerControl will offer these via plug on the MerControl or via pigtails on the newer Mercury controls.

The stator pulse is on either of the yellow wires that go to the rectifier. One of these should connect to a grey wire or perhaps a brown wire. A 1979 motor is about the time the wiring colors changed, so look at the choke solenoid. If that wire is grey, the pulse to the tach will be brown. If the choke solenoid wire is yellow/black, then the stator pulse to the tach should be grey.
Click to expand...
I do have a brown wire coming off the rectifier that I’m have hooked onto tach signal terminal and, a battery wire and ground on the other two terminals. Nothing happens. Is there any way to test the tach on the bench?
 
BWR1953

BWR1953

Admiral
Joined
Jan 23, 2009
Messages
6,328
Kissdude said:
I do have a brown wire coming off the rectifier that I’m have hooked onto tach signal terminal and, a battery wire and ground on the other two terminals. Nothing happens. Is there any way to test the tach on the bench?
Click to expand...
You can test the tach with a battery charger. Do a google search and you'll find out how.
 
K

Kissdude

Petty Officer 3rd Class
Joined
Sep 7, 2024
Messages
98
Chris1956 said:
Mercury tachometers need +12VDC, ground and stator pulses to operate. Normally a MerControl will offer these via plug on the MerControl or via pigtails on the newer Mercury controls.

The stator pulse is on either of the yellow wires that go to the rectifier. One of these should connect to a grey wire or perhaps a brown wire. A 1979 motor is about the time the wiring colors changed, so look at the choke solenoid. If that wire is grey, the pulse to the tach will be brown. If the choke solenoid wire is yellow/black, then the stator pulse to the tach should be grey.
Click to expand...
After doing some testing, I noticed that my battery wasn’t getting higher charge then 12.7 volts. Checked the rectifier and it’s bad. Could this be why my tach doesn’t work? Thanks
 
merc850

merc850

Commander
Joined
Jul 7, 2010
Messages
2,052
Check the AC voltage across the yellow wires it should be 13+ and go up when the motor speeds up.

Rectifier testing.
rectifier-testingsmall.jpg
 
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