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Electrical - Tachometer Adapter

Page history last edited by MORG_kw 9 years, 1 month ago


The VStar 1300 has what is called a single-fire ignition. That means that only one coil (a single coil) fires on each compression stroke. If you connect many different brands of tachometer to either coil, the tach will read half of the actual RPM.


A double-fire or dual-fire ignition, like many of the older bikes that do not have an ECM (computer) fire both coils on each compression stroke. That means a tach connected to either coil on those bikes will read the true RPM.


Of course you would not want to connect the two coils together since it might destroy the ECM. So, what do you do?


You can buy tach adapters from several sources for about $30 to $100, or you could make your own for less than $5.

Here's how.




Go to Radio Shack and buy two of these "things" - (RS #64-3064) http://www.radioshack.com/product/index.jsp?productId=2103503


Unplug the negative coil wire on each coil (orange wire on one and red/gray on the other).  Do not unplug the red/black wires. Plug one of those "things" (RS #64-3064) onto the coil terminal where the wire you just unplugged was located.  Plug the wire back onto one of the terminals on the RS #64-3064. You might have to use a pair of heavy duty wire cutters to trim the terminal on the RS #64-3064 to accept the coil wire plug.  Now the bike is still in a stock configuration but you have a point on each coil where you can make a connection without cutting any wires.


Time to make the tach adapter. While at RS go ahead and buy two 1N4004, 1N4005, 1N4006, or 1N4007 or equivalent diodes. Also buy two 100K ohm resistors. 1/4 watt or 1/2 watt is OK.


Lay a diode and a resistor side by side on your table and twist the leads together. The diode and resistor are now in parallel. You can now either add a short length of wire to one end of each diode/resistor or you could solder a terminal (RS #64-3058, etc.) directly to the pair.


Last thing to do is to connect the tach wire to the other end of both diode/resistor pairs.

"The end of the diode with the silver band must be the end that is connected to the coils - not the tack lead."
This ensures the diode is connected properly.


I put some heat shrink tubing over each diode/resistor pair before I soldered them to the tach wire. Then I put heat shrink over the whole mess.


This is a great beginner's electronic project.



Jack ......along with some very helpful updated information provided by Uncle Bob

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