1973-mercury 500-50hp Tach question?

[bigsidster]

I have a 1973 Mercury 500-50 hp-2 stroke---4 cylinder outboard.I have a Power Fist Electronic LED Tachometer 0 to 8000 rpm.It is a TRISCO brand.It is a 12VDC and has a setting button to set it for 4,6 or 8 cylinder.Has 5 wires coming out of it.BLACK is ground to -negative battery terminal,RED is tach power wireto ignition ON (run) position.ORANGE is memory LED and goes to battery +positive.WHITE is night light and goes to light switch.GREEN is the Tachometer signal wire and connects to signal source.

2 questions?
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Can I install this tach and use the "4 cylinder setting" and get a correct reading?

If I can,where do I connect the GREEN tach source wire?

Thanks for any help you can give me.

 

[bigsidster]

Re: 1973-mercury 500-50hp Tach question?

Please---somebody with tach knowledge please help.

 

[Barnacle_Bill]

Re: 1973-mercury 500-50hp Tach question?

That sounds like an automotive tach. It will not work properly with an outboard. 2 cycle vs 4 cycle. Input for the tach is a gray wire in the harness.

 

[pman7]

Re: 1973-mercury 500-50hp Tach question?

I can't confirm whether or not you have an automotive tach.

When you get the right tach your sender wire should hook to either of the leads (yellow wires with red stripes) on your rectifier that come from your stator/alternator. There is a third lead on your rectifier that has a red wire and that is the only wrong wire.

There is no wire in a stock wiring harness that hooks to these leads. You can rig the wire through your harness but most people run the sender wire straight to either of those yellow wire leads on the rectifier. The rectifier switches the current produced by your stator from AC current to DC current and sends it out through the red wire side of your rectifier.

The marine type tachs read the number of pulses from your stator. Since your tach says cylinders and not pulses I would speculate that you do indeed have an auto tach as the previous poster said.



ps: The information I gave you is for my 71 Merc500. I believe your setup is the same. I'm not certain but I think it is so.

 

[bigsidster]

Re: 1973-mercury 500-50hp Tach question?

Thanks for responding PMAN7.Looks like it is an auto tach so I wil have to trade it for an outboard tach.