79 40hp tach Q

[djcheez]

I found a 3 pin harness to plug into throttle assembly, and bought a telefax tach . I've got the wiring correct but getting no rpm signal on any of the settings. Is there a way to use a multimeter or some other method to test for an rpm signal? I'd like to test the wiring all the back to see if the issue is there.
For this particular engine, there isn't anything else needed to run a tach is there ? In my search for tachs I saw "tach modules" and wasn't sure if maybe this was something I needed and was the issue ? Just looking for any suggestions please

 

[GA_Boater]

Using a meter, make sure the IGN stud has 12 volts when the key is on and the GND stud is 0 ohms to any other ground. With the motor running, the SEND stud will have AC voltage. The switch should be set to 6P.

 

[djcheez]

Thank you, I'll give that a try

 

[merc850]

If that's a new tach and not a Quicksilver part one you have to run a separate wire from a yellow wire on the rectifier to the sender post on tach. Set the tach at 6p. Connect the black and white wire to + and - and the light to your running light switch.

 

[djcheez]

Just tested and everything checks out ok. Went to Teleflex to look at trouble shooting and found in fine print "Mariner 30 & 40 HP (2 cylinder) engines require a Module (Mercury P/N 17461A2) when using any of these tachs.". Looks like I need a module

 

[djcheez]

Turns out this part. 17461A-2 is no longer made and tough to find. I'm wondering if all this is is some kind of resistor. That I can make/ buy elsewhere ? Any ideas anyone?

 

[merc850]

Just hook it up to the alternator I've done it in 2 boats and it works. It is probably some sort of counter that detects and sub-divides the pulses over time (minutes).

 

[djcheez]

Understood , will just do that. Thanks for your help

 

[merc850]

Make sure that it's well insulated from any parts of the motor, if it shorts to ground it could catch fire.

 

[djcheez]

Last question please. When tapping into one of the yellow wires on rectifier, can I route this (within engine compartment) into the wire that would end up as the current tach signal wire coming out of throttle control box, thus eliminating running a single wire out of engine to tach? Or best to just run the wire all the way up?

 

[GA_Boater]

As long as the harness to the remote has the tach wire, it should work, DJ.

Connect a meter to the Send stud on the tach and the tach wire inside the motor. Check for continuity on the ohms scale. If you have 0 ohms, simply connect the tach wire from the side motor connect to either of the regulator connectors from the stator. That's a much better way to tie in the tach wire.

 

[djcheez]

GA- after inspecting further, there is a brown wire attached to post on rectifier with one of the yellow wires. I tested continuity to my tach send post and had 0. Ohms. I have a cheap digital tach that I connected to the end of the signal wire and it read fine (I just don't like the digital one) so I know I'm getting a signal there that can be picked up. My question now is , the wiring diagram doesn't show a brown wire attached to rectifier so maybe someone has already done this??? But not sure what else to look at , maybe tach is bad? It is a discontinued unit

 

[djcheez]

No Title

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[djcheez]

Update

engine serial 5366788 possibly a Japanese built with a lighting coil magneto ignition system, no alternator. Im guessing this is why im having so much trouble. Tapping into yellow wires on rectifier has already been done as the brown wire i mentioned is the same brown coming out of remote control.
I tracked down part number 17461A-2 after having to pay to talk to Mercury "Tech Vintage Hotline". I installed the module which is nothing more than a resistor , and tach only has intermittently worked a couple times. If i have researched and understand correctly, this part number may not even be for this particular Jap. built engine, but a specific tach from Mercury that is NLA. Even if i could find this, it would be $300+ and thats not worth it.

GA - The suggestions you offered were for engines with alternators therefore wouldnt work for my application correct?

I may just take the engine to a shop and have them figure it out.