Tachometer installation help on '11 VN 900

[diamondhill]

I purchased this new tach from BKRider and the single fire adaptor from e-bay. I have my tach hooked up to an external 12V supply and the tach does initialize (0 to 8K and back)) when it is pluged in.
Each coil shoul have a - and a + and the adaptor wires should go to -
With the engine idling, when I measure from the bike ground to any of the 2 wires on each coil, I get a + reading on all 4 terminals( one red and one black). I did it again and the same + + + + readings. I know that the black should be the - and I hooked up the adapter to these terminals.
Start the engine but the tach stays at 0...
What am I doing wrong here and why the + reading from both terminals of the coil? Any help is more than welcome.
[/IMG]

[C00lCountry]

Well from what I remember on most coils they work like this.
Power to the hot side
Wire to plug for spark to travel to
Ground wire is controlled by points or electronic ignition to tell it when to spark.
I not sure details on tach.

[diamondhill]

Thanks, but I was asking why do I get a + reading on each of the coil terminals.
I think I will need a electrical diagram to find out.

[C00lCountry]

If the ground is not constant, then it is an open circuit.
When you touch with test light it is complete circuit then for reason you get current on both sides.

[diamondhill]

I measure 12 V with a voltmeter. Bike ground to each of the terminals on both coils gives me ++++. WTF?

[sfair]

Twist tach power and light together and connect to coil red wire. (common between two coils)
Connect adapter to other two coil wires.
Connect ground to convenient black/yellow.

Your meter reads 12v on all coil leads because it cannot react fast enough to register negative going pulse with bike running.
Engine not running will give 12v on both sides of coil.

[diamondhill]

Great ideea and thank you much. I will try tomorrow morning.
And just to aviod making any connections inside the headlamp can I just connect the tach's black wire(-) to the bike's ground(frame) and not the battery?
Also, because would be easier I will connect tach's power to one coil(+) and light wire to the other coil(+)

[sfair]

If you can find a good frame ground, you will be off and running!

[diamondhill]

I will connect the ground wire on the bottom screw of one of the coils. And do you think the reason it did not work is the fact that I had the power from the external power supply? Because this is the only thing I will do different now? Thank you again.

[sfair]

Hmmm, with seperate tach voltages (12 volts and signal) plus seperate grounds, it may be a problem. At the very least, supply ground would have to be referenced to bike battery ground.