Merc 650 ignition

[OCboat]

I just recently purchased a 1968 Mercury 650 serial #2446837 along with a Seloc repair manual. According to the manual my motor should have a type III ignition but the switchbox in my motor is the same as in a type II as is the wiring. Is my Seloc manual wrong or is it possible that I have an ignition from another motor? I'm also having trouble locating an original tach for this motor and have read that the brown wire can be moved from the switch box to one of the yellow wires on the rectifier to use a different tach. The only brown wire on my switch box goes to the mercury switch, any other suggestions that would enable me to use a different tach? The wires that lead into the switch box are as follows. Top - red wire to ignition driver: second from top - blue to ignition driver, orange from engine harness and brown to mercury switch: Third from top - white to ignition driver: last - black and green to coil. Thanks.

 

[ricksrster]

Re: Merc 650 ignition

You can run a separate new wire from either yellow wire post on the rectifier to the signal post on the back of your new tach. Set the little switch on the back of the tach to 12 pole or 6 pulse. Connect 12v+ post of tach to 12v+ post on ignition key on. Ground post to a ground neg. post on battery. Connect the light post on tach to your nav, lights. The tachs usually come with a complete set of instructions.

 

[OCboat]

Re: Merc 650 ignition

Thanks ricksrster. I picked up a used tach at a marina and wired it like you described. It worked well except for rpms below 800. When at idle, the needle would drop to zero. When the throttle was increased the needle would finally register starting at 800 and then work fine above that point.