Help me install this tach on my 1500 Merc- photos and plug

[supervetteracer]

1974 Merc 1500 Tower of Power motor serial number 3503374.

This is the controller:

It has a plug on the end for this cord.

It has a Black, white and green wire:

And this is the tachometer:


Is this a 10 or a 12? Do you know which wires go where?

[perfmarine1]

Black is ground- white is I for ignition-green is S for sending. To check plug in and see if you have 12 volts between black and white wires with key in run position. That will test it.

[supervetteracer]

Just tested. I have 12v from the black / white. If I go black and green I show 6V.

Tried hooking it up this way and got nothing. Then tried reversing the white / green - Nothing. Then tried switching from 10-12 pole-- Nothing.

Guessing my issue may be from the motor. But the black white did read 12v and the black green read 6v.

Any thoughts?

[supervetteracer]

Been fooling around trying to make the stock tack work but have not had any luck. I just purchased one of those small digital hour meter / tachometer units. It has it's own battery and when I wrap it around the plug wire like I am instructed it gives me a very sporadic reading. Like over twice what the RPM should be. I'm wondering if this new two or four stroke tack is too new for this 1974 Mercury 1500? This motor does has a distributor cap and rotor. Is my motor too old for the newer tack to work?

Someone here should have some insight on this. Throw me a bone, even if it's just a guess. I'm running out of ideas and I need a working tach so that I can buy the correct prop.

[powerabout]

on those old Mercs the tach wire came from the pak
If you use a alternator tach you will need to shift the wire at the powerhead to one of the rectifier wires

[supervetteracer]

on those old Mercs the tach wire came from the pak
If you use a alternator tach you will need to shift the wire at the powerhead to one of the rectifier wires

So which of these wires do I need to connect to?

[powerabout]

first you need to determine you have a alternator tacho then if so you need to connect to the stator which if my memory serves me were the 2 wires that seem to be missing from the plastic 2 terminal block in the second photo just aft of the crankcase split, level with the positive terminal on the starter

[crazy horse]

It looks like someone already moved the wire. The wire that gets moved is the brown one on the four terminal side of the switch box. That's how my 76 XS is wired for my alt. tach. It looks like someone replaced the yellow wires that come down from the stator. They are black and red on your motor so That's where I'd start looking.

[transomstand]

What that motor needs is a nuther dozen butt connectors

This is an illustration of how to wire an ADI tach in an older inline. The difficulty here becomes readily apparent, wires have been cut, moved, changed to God knows what...

The brown wire should be on the "G" terminal of the engine connector plug if you want to trace it back. Where the stator wires are is a mystery, but without them going to the rectifier, I don't see the tach working or the battery getting charged.

[transomstand]

Not the best scan, but should be some help.

[milkdud]

man the wiring is a mess on that one. which is common. they get patched together over the years.


If its a alternator tach you can get you signal from one of the rectifier leads.

If its a switch box tach there is a screw that it for the tach. Usually a grey wire goes to the tach post on the switch box.


If it were me id seriously think about putting a new wire harness in it.

Conrad

[supervetteracer]

First off a Big THANK YOU for the help. Especially Transomestand Heathen. I do appreciate the diagrams and such.

It appears that the tachometer that I have (NOT THE ONE PICTURED) is for a newer two stroke. And although the directions seem pretty simple (Wrap a wire around any one of the spark plug wires- it's a one wire hook up thing) I'm guessing that it will not work on this old of a motor. I'll try and attach it to where you say the "brown" wire connects when I get home.

Other than that I feel that I may be in over my head. This motor runs great. And it charges the battery. I don't think that I am getting all the RPM out of it that I can so I really need to have a tachometer. But I don't want to risk having to re-wire the entire motor just to get the tach to work.

Thanks again for all of the help. Would really like a direction like, wrap it around this wire or connect it to this. But I understand that given the amount of engineering this motor has had done to it over the years that it may not be this simple.

[milkdud]

Buy a cheap 12 pole alternator tach(they are adjustable usually) off ebay and hook the signal wire up to one of the wires coming down from the stator to the rectifier.

The only other two wires on this type of tach are ground and hot. The hot is something you tie into your switch so its not drawing power when you shut the motor off.
Very simple. I switched to using this type of tach vs the old style that ran off the switch box.
I've tried the tiny tach stuff too and they work rarely on my outboards

Here are some options:

http://www.ebay.com/itm/FARIA-TC9011...199be0&vxp=mtr

http://www.ebay.com/itm/TELEFLEX-682...3b14ee&vxp=mtr

http://www.ebay.com/itm/FARIA-TC9653...d71124&vxp=mtr

As long as it has a 12 pole option it will work on your stator.

c



C

[supervetteracer]

Tried the 12 pole tach I had on it. Hooked the + and - straight to the battery and ran a wire to the S. Touched pretty much everything I could with the S wire and got nothing. Then switched poles and re-tried. Guess it's back to the drawing board. Can't believe it's this tough to get a tach to work. Problem is that I NEED it to work so I can prop the boat correctly.

Is there an easy guaranteed way I can test my RPM? Just need to do a couple WOT sweeps to decide on a tach.

[transomstand]

I see no reason why you couldn't just run a wire from a yellow rectifier terminal for the tach signal.