Adding tach? 75 Merc 402 40hp

[vupilot]

Hello,

I want to add a tach to my homebuilt boat so I can be sure I have the right prop on my 1975 402, 40hp Mercury with MerControl. I bought this harness to connect a tach to the control box plug. http://cgi.ebay.com/ebaymotors/NEW-MERCURY-MARINER-CONTROL-BOX-TACHOMETER-HARNESS-/300216562250 I hope its the right harness.

Now I am confused on what tach's are compatible with my motor/control box.

What Pole is my motor? 12?

Do I need a coil or alternator powered tach, are most tachs compatible with either one?

Would this tach work for me?
http://cgi.ebay.com/ebaymotors/TELE...5219865QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

Thanks,
Chris

 

[merc850]

Re: Adding tach? 75 Merc 402 40hp

The wiring harness will work and the tach will too if set to ALT but you will have to switch the salmon wire to a YELLOW wire on the rectifier: see diagram the SALMON wire seems to be part of the ignition and jumpers to the BROWN wire in the engine plug. The BROWN wire is the tach signal wire in the tach wiring harness, you might have better luck running a separate wire from the rectifier to the ALT terminal on the tach and just use the wiring harness to provide power and the light.

 

[vupilot]

Re: Adding tach? 75 Merc 402 40hp

Thanks, Is there a tach I could use without modification to the wiring?

 

[merc850]

Re: Adding tach? 75 Merc 402 40hp

Yes an original 1975 Quicksilver one but I don't know where you will find one.

 

[vupilot]

Re: Adding tach? 75 Merc 402 40hp

Is that the only kind that doesnt require the wiring mod?