mercruiser 350 mag mpi tach wiring help

staticbags

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Aug 17, 2017
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I have searched for hours and need some help. I bought a used 2004 ski centurion direct drive with a mercruiser 350 mag mpi 5.7
serial # OM396936
Tach did not work when i purchased but i'm trying to fix. I am not sure if tack wires are hooked up to engine where they should be. I found 2 loose wires:
1 grey with female connector attached and rubber plug in it
2 black wire looks like ground. both zip tied together up toward front of engine and not much extra wire. I can not find anywhere they should go. Or are they just dummy wires and there is the real tack wire plugged into the EFI or somewhere else
see pic
I am not sure if tach is good, but feel these two wires should go somewhere. I can't find any pics or video of where they go.
please help.
jeff h
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
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welcome aboard

tach signal wire is grey, goes to the - side of the coil

the two black wires in the front are for the outdrive lube monitor. you have an inboard so you dont have a lube monitor

if you have smartcraft gauges, then the gauges communicate with the motor via a J1939 canbus backbone and there are 3 wires (transmit/receive/ground)
 

alldodge

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Howdy Jeff

Don't thing those wires go to the tach because you have the HVS distributer. The tach feed should come from the coil molded connector up to the helm. Look on the back of the tach to see if any of the wires are disconnected or damaged. Turn key ON and see if you have 12V on the purple wire.

Solid gray is power to sensors, and gray/white is external tach lead
 

staticbags

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Aug 17, 2017
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ok behind tach looks ok. there are two large places to plug in wires. only one is used. this is 3 in1 inst. (tach, temp, oil, light)
I believe it is stock centurion 04 guage (faria gt0030b)
there are some unconnected wires just behind the dash but i don't think they matter to tach.
i'll try to post pics. if it won't llet me here, i'llpost my email and can send you them then.
 

alldodge

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It use to be 3 post before you can upload pics, but then something changed so don't know how many it takes but think its under 10. You could use google docks or something like that
 

alldodge

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Your using photobucket (3rd party host) like google docs and others. My comment was for uploading pics to this site. To link pics from another site just select the image icon, then post in the URL section. PB is stopping all hoistin so its a matter of time before your pics are gone
 

staticbags

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Aug 17, 2017
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update: pulled the panel out and unpluged tach cluster. tested the plug that plugs into tach and had 12volts at the plug. This makes me think its the tach itself that is bad. any thoughts?
I put two wires on 6 volt batt and touched all the pins coming out of instrument. I could make oil press and water temp needles move, but tach never moved. I re plugged the instrument back in boat plug and turned key on, and every needle swept except tach. its frozen in place. but again, the pin to it has 12v and the two pins to water temp and oil press seemed to have 15v. (i am NOT good with those meter checkers.)
 
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