Need help connecting digital tach signal pickup to coil

[JayR]

Hi guys. I'd appreciate your advice, especially if you have connected the yellow tachometer signal pickup wire from an Acewell Speedo/Tach unit to a stock 1981-1983 ignition coil.

The manufacturer's instructions provide two options; 1) wrap the end of the yellow pickup wire around the spark plug wire 2-5 times, OR connect the wire directly to the ignition coil.

QUESTIONS
1) Do I connect the yellow wire to the positive or negative coil terminal?
2) How exactly would I connect the yellow wire to the + or - coil terminal? I do not know where either is located on the coil (please see drawing in next post).
3) the manufacturer provided a 1Mohm resistor to help smooth out the signal, how do I use that? Do I solder it to the yellow wire in-line? Does it matter which direction the resistor is oriented?

Note: I have the signal pickup wire connected now using the 2-5 wrap around method and the RPM readings are all over the place jumping around wildly at idle and on the road.

Also, the manufacturer diagram below references a CDI - for our purpose that should read TCI.

Thanks for your time to read this!

 

[JayR]

For reference, this is my stock ignition coil. Where should I connect the yellow signal pickup wire? I know, probably a very basic question

 

[TwoManyXS1Bs]

Here's Glennpm's thread:

http://www.xs650.com/forum/showthread.php?t=33782

 

[JayR]

Thanks TwoMany. I did find that thread and read it over a couple of times. Maybe I was having a low IQ day, but it seems the thread advises to 1) connect the signal pick up wire to the negative coil terminal and 2) use the 1Mohm resistor.

What part of the coil is the negative terminal? Is it one of the two posts that are used to mount the coil to the frame, or do I need to unscrew one of the fasteners that secure the spark plug wires to the coil and attach the wire there, or do I need to tap into the wire connector that connects with the TCI somehow?

Cheers !

 

[grizld1]

Oh yeah, plenty of insight there from guys who've never set eyes on the instrument. Connect the signal wire to the signal side of the coil. On negative ground systems, that's the negative primary terminal; does it make sense that you're not going to get a signal off the 12VDC power terminal? Use the resistor in the kit unless you want the tach to spike erratically. If readings spike with the resistor in the line, add another one; with a Boyer ignition, I had to use a pair of 1 mega ohm resistors befoere things calmed down. Support the resistor(s) with 3 or 4 layers of shrink tube if you want the solder joints to hold.

Just read your last post. The positive primary terminal is the one that's hooked up to 12V power. The negative primary terminal is the one that takes a signal from the contact breaker points or from the control unit of an electronic ignition. On machines with positive ground charging systems (older Brit bikes, for example), it's the reverse--negative power, positive signal.

 

[JayR]

....Use the resistor in the kit unless you want the tach to spike erratically..... Support the resistor(s) with 3 or 4 layers of shrink tube

Will do. Does the resistor need to be oriented one specific direction or does it not matter?

... The negative primary terminal is the one that takes a signal ....from the control unit of an electronic ignition.

OK I think it's penetrating my skull now. I looked at a few wiring diagrams, is the negative primary terminal the terminal with the red/white wire in the picture attached? If so do I simply solder the yellow Acewell signal pickup wire to this post, with the 1MOhm resistor inline?

Thanks Grizld1 and TwoMany

 

[grizld1]

No. The R/W wire is 12V power from the kill switch and feeds the positive primary terminal. Connect the tach to the other wire using a 2-way connector.

 

[JayR]

No. The R/W wire is 12V power from the kill switch and feeds the positive primary terminal. Connect the tach to the other wire using a 2-way connector.

Got it now, thanks very much!