Tachometer Installation

[greatoutdoors]

Hi, I have a 70 Merc 40hp model 400. I want to install a tach. Could anyone provide me with instructions on how to do so? Also, does this particular motor have an alternator? I just got it and haven't gone over it thoroughly yet. Thanks.

 

[jimg984]

Re: Tachometer Installation

yes, has a charging system, look for two yellow wires coming from under the flywheel, they hook to a device called a rectifier. the signal wire wire for the tach would hook to either of one of them. next the tach would need a hot wire from the iginiton switch. also gotta have a ground wire attached to tach.
then if you wanna have a light in the tach that would come from the light switch
hope this helps good luck you can do it

 

[greatoutdoors]

Re: Tachometer Installation

yes, has a charging system, look for two yellow wires coming from under the flywheel, they hook to a device called a rectifier. the signal wire wire for the tach would hook to either of one of them. next the tach would need a hot wire from the iginiton switch. also gotta have a ground wire attached to tach.
then if you wanna have a light in the tach that would come from the light switch
hope this helps good luck you can do it

Sounds easy enough. Let me clarify for myself, as I'm not that bright. Now for the light in the tach, can I just run a wire from the tach to the toggle that controls my night running lights so when I flip them on the tach light would come on? When you say the hot wire for the tach should go to the ignition, should I splice into the wire for the starter or somewhere else? Can I just run the hot wire to my cranking battery and then ground on the motor block or the neg terminal? I'm not that super with electrical but I can get by with some direction. One more question, can I use any tach (for a car) or do I need a marine type tach. Thanks.

 

[jimg984]

Re: Tachometer Installation

nite light switch yes
auto tach no
hot wire for tach should be hot only when switch is on
ground could from engine, neg battery, or existing ground for night system
the later should already be under the dash

 

[greatoutdoors]

Re: Tachometer Installation

nite light switch yes
auto tach no
hot wire for tach should be hot only when switch is on
ground could from engine, neg battery, or existing ground for night system
the later should already be under the dash

Thanks so much, so what would be the best wire to splice into for the hot wire?

 

[Silvertip]

Re: Tachometer Installation

If you have any other gauges, connect it to the +12 volt terminal on any gauge. Ground is wherever you find it. At the fuse panel, engine block, battery negative, or at the ground terminal on any other gauge. You don't need to run wires all the way back to the back of the boat. +12 volts and ground are available at the console via the control box.

 

[greatoutdoors]

Re: Tachometer Installation

Thank You.