adding a Tach

[dbergman]

I have a Merc 50, 4 cylinder and want to add a tach and ampmeter (also a speedo and fuel gauge) while I'm restoring this boat. Does this model require a special tach or ampmeter or is plain vanilla OK? Also which wire do I use for the tach?

 

[ricksrster]

Re: adding a Tach

Use any one of the two wires going to the rectifier from the stator.run this wire to send on tach. Hook up a pos key on from ignition to pos or ign on tach, light wire, and ground. Set tach for 12 pole 6 pulse. Usually instructions come with instruments and give different instructions for the model motor toy are using.

 

[Silvertip]

Re: adding a Tach

You would be well advised to install a voltmeter rather than an ampmeter. Ampmeters (or ammeters if you prefer) are wired in series with the positive lead from the battery so it indicates both charge and discharge "rates". Therefore heavy gauge wire must be routed to the console and back to the battery. A voltmeter tells you what the charging system voltage is and can be connected to a 12V source at the console. Its simply a more useful gauge. Speedometers are pitot driven and are not engine specific -- in fact there are no connections to the engine unless the engine has a built-in pitot. Fuel gauge is also not engine specific. Your tank needs a fuel level sender that matches the gauge.

 

[dbergman]

Re: adding a Tach

Thanks for the responces. I believe I will go with the voltmeter. The Moeller permanent fuel tanks is equipped with a Stewart Warner electric sending unit. Would you happen to know if this is compatible with say a teleflex gauge? What is a good source for gauges?

 

[ricksrster]

Re: adding a Tach

It should. How the sending unit works is that it is a variable resistor. the fuel gauge is like a voltmeter but graduated in E,1/4/1/2, F...instead of volts. Like Upinsmoke said about using pos from the console, I would use Pos wire from ignition with key on so the gauge works only with the key on so it's not drawing current all the time. Same with a voltmeter, connect to key on. I use a voltmeter instead ofam ammeter. when running you will show from ~13.3 - 16 volts as your battery is charging. dropping below 12 - 9 might be too much load or you're not charging. speedometers are easy. Pitot tube and light wiring.

 

[dbergman]

Re: adding a Tach

Can I use the same inginition with key on in series for the tach and the voltmeter? What wire size should I go with. I'm thinking of rewiring thru a fuse panel for the gauges, adding a bilge pump and redoing the lighting wiring (it's a real rats nest at the moment).

 

[ricksrster]

Re: adding a Tach

You want to wire the tach and volt meter in parallel. You don't need very heavy wire because these are low amps. I used #18 on mine. The bilge pump you probbly want to wire back at the battery. wiring the bilge pump depends on if you want to use a float switch or just an on off switch. On mine I used a float switch with a switch on my dash for off, auto, and momentary on. When you buy want follow the instructions supplied with the items.

 

[dbergman]

Re: adding a Tach

Thanks. I understand what you mean. Do the lights use #18 also?