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Jason, Marine Mechanic
Category: Boat
Satisfied Customers: 15635
Experience:  Degree in Marine Technology. Gas and diesel marine mechanic.
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I am ***** ***** I have a mercruiser 470 which has been

Customer Question

Customer: hi jason. I am ***** ***** I have a mercruiser 470 which has been rebuilt and put in my old launch. I need help wiring the tacho
JA: Thanks. Can you give me any more details about your issue?
Customer: my tacho is a wema brand inclusive of hour meter. I hve power to it but am unsure how to connect mytacho. which wire is on the merc wiring loom as the sender for the tacho
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Submitted: 1 year ago.
Category: Boat
Customer: replied 1 year ago.
the engine still runs the stator system. Is it possible as it has no alternator to bypass the loom and go onto the negative side of the coil. I have connected this and had the tacho running but am unsure what to set the tacho at to align with the coil ie rev ratio. the tacho is wema with inbuilt hour meter. It is programmable on the back of the tacho by pushing a rubber button and goes up an down in .5 increments.
please advise
Expert:  Jason replied 1 year ago.

Hi Aaron, my name is ***** ***** I will be helping you today. I would need to know the exact model number or part number of the tach that you have.

Customer: replied 1 year ago.
Hi Jason,
Tacho is a wema iqhb-bv-8kl
Hope this helps
Expert:  Jason replied 1 year ago.

unfortunatley it does not. Is that the number on the back of it? I tried punching that number into google and got no results. Are there any other numbers on the tach, or the box the tach came in? Can you take any pictures of the front and back of it?

Customer: replied 1 year ago.
That is the model number I google it and had no issue
Expert:  Jason replied 1 year ago.

I don't see it. Can you share the link with me?

Customer: replied 1 year ago.
HI Jason,
please see below and copy and past into your browser, i look forward to your response
Expert:  Jason replied 1 year ago.

Hi Aaron. To be honest i'm not sure if this tachometer is going to work for you. It states in the instructions "this tachometer can only be used with an alternator with a W terminal"

That being said. Just for the heck of it. Have you tried hooking it up to the gray wire that is in the engines harness?

Customer: replied 1 year ago.
Hi Jason I've tried the gray in the loom but there is no signal. How do I check if the gray is sending any signal
Expert:  Jason replied 1 year ago.

You would use either a standard tachometer or a lab scope (oscilliscope) to check for an output signal. Do this as a test. Start the engine up. And then when it's running take the gray wire and touch it to ground. If there is a signal the engine should stall. Let me know if it stalls or not.

Customer: replied 1 year ago.
I can get signal from the negative side of the coil. Would the ratio setting of 2.0 be correct to be the same as the revolutions of the engine. If not please advise the setting i should use and would this prove to be acceptable
Expert:  Jason replied 1 year ago.


This tachometer is not designed to work with you engine. It 'might" work, but it is not designed to. With the engine at idle, what does the tach read with it set to 2.0? What does it read when set to 4.0? It might not be 100% accurate but you might be able to use it if it is "close enough".What do you get for readings


Expert:  Jason replied 1 year ago.

Hi Aaron, just checking in. Any luck/progress?

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