Installing a tachometer

[steffanf]

I have a 2007 Lund 1425 Classic SS with a 40 HP Merc 4-stroke. The boat came from the factory without a tachometer. I do want to install one, but I have a few questions. First, can I use any automotive tachometer on the market or does it have to be a marine tach? I would assume the RPM range of the 40 HP Merc falls below 8000 RPM's, but is the car tach suitable? Maybe a marine tach is suggested because it is waterproof? Also, there are several capped off (unused) wires under the dash and the under the throttle (in rod locker). There is also the end of a 2 or 4 wire connector under the dash. Could it be that the boat is already pre-wired for a tachometer? If so, which wire would be the correct one? Barring all this, if I have to wire in the tach myself, where exactly do I connect it to? I have done car tachs before, but is there someplace different I need to know about inside a 4-stroke outboard? Any and all help is appreciated...

[boatfixer]

You are going to want to use a marine outboard tach, an auto tach will not work the same.

What color are the wires you found? the tach signal lead is gray.

[Valv]

You should have 4 wires for the tach.

Purple + (under key)

Black -

Gray (signal from motor)

Blue illumination

You cannot use an automotive tach. Be sure your motor (not just the boat) is setup to have a tachometer. Newer units mostly have it

[steffanf]

OK... I will make sure I get a marine outboard tach. I assume they are available at the big "C" store. Also, I will check the wires again and see what colors they are. I may post some pictures to make sure I'm looking at the correct wires. I am assuming that most of the boats in a certain class (in this case, Lund Classic series) use the same exact wire harness. Now, how would I know if the motor is set up for a tach? The motor is a 2007 40 HP Mercury 4-stroke. I thought all motors can accept a tach?

[steffanf]

OK. I got some pictures. I will identify the colors of each wire. In this photo, you see the black connector located under the console. It is not being used, and it only has one black wire associated with it:

This view is from another angle showing all the wires underneath the console. As far as I can tell, the aforementioned black connector is the only one that is not being used:

On to the main bundle. There are several unused wires located down in the rod storage, just below the throttle. The colors are as follows: Red; Green/White; Yellow/Black; Tan/Blue; Dark Blue/White. The black connector with all the wires coming out of it has a MERCURY symbol on it with the wording: "SmartCraft".

So... is the boat pre-wired for guages? And, which do I use for the tach?

[steffanf]

Guess I really stirred up an enigma! Apparently even the boat manufacturer doesn't know the answer? They (Lund) are telling me that there should be some unused wires behind the dash coverplate. However, when I look under the console itself, I only notice the aforementioned black wire with connector. When I asked Lund about the wires under the throttle, they had no idea what those were for! The colors do not match anything they are aware of.

So, I guess for my next step, I will take off the dash cover plate just to make sure I didn't miss anything. Then I guess I will try to contact Mercury to see if THEY know anything.

[boatfixer]

Thats because it's mercury's wire harness, not Lunds. The one labeled "Smartcraft" is just that, for pluging in Smartcraft gauges.

[marine_man]

Let's back up for a second; I presume you don't have any gauges now?

marine_man

[steffanf]

No... I do not have any guages at all now. It is sounding like I need some sort of harness now. I'm hoping it is just something that plugs into the big "SmartCraft" bundle in rod storage and runs up to the dashboard. From there, I assume all I have to do is wire plug the tach into the harness.

[steffanf]

WOW! This is getting to be a joke! I just called Mercury... you know... the ones that make the motor, wiring harness and the throttle control? They gave me some parts and serial numbers for what I would need. First, I would need some sort of wire harness that goes from the throttle control to the console, and then the Mercury tach. The price the Mercury rep quoted me was $190 for the harness and $375 for he tach!!!! What the heck... $565 for a simple tach, and that doesn't even include installation?!? No way! I have a feeling the person at Mercury doesn't know what he is talking about. I plan on getting to the bottom of this, but obviously I am not talking to the right people...

[steffanf]

OK... I have a theory. I am going to test it and see what happens. I got a used tach. I don't know what kind of boat it is out of, but I was told it works. It goes from 0-7000 RPM and has multiple settings in the back. What setting do I need to use for my motor (2007 Merc 40 HP 4-stroke)? Also, I plan on wiring it with 18 AWG wire. Would this be sufficient for this guage? I'll let you all know what happens after testing...

[harvey lee]

Installing a tach isnt that bad but if you don't have a wiring harness, then it is a bit more money and work.

[RuKiddingMe]

I would recommend taking the part numbers you got from Mercury and heading over to that BIG OL Auction websitre that starts with an "E". I just did this for my SmartCraft ready Merc, off that HSOforum I was able to get the gauge and the wire harness for about $200, more then half of what Merc wanted to sell that stuff to me for.

I'm not sure if the 4 strokes are smartcraft or not but if they are you should just go that route an all in one solution like an SC1000 (digital gauge part number 79-879896K21) gauge.

RU

[moderation]

The only settings that I am aware of on the back of the tach are for the number of cylinders. Sounds like they are pretty high on the price of the tach.

[boatfixer]

12 pole setting is what you need on the tach.