Sunday, June 28, 2009

wiring tach part two

OK, now for the head scratching. I could use some help here! This bike does not come with any facilities for tach output management, so I'm parsing their instructions on how to patch the sensor into my engine coil directly:

If you wish to connect the ignition coil, the SPA tacho is fully protected. It will connect to any coil including magneto's and is not damaged by reverse polarity. Connect black to chassis, and red to the ignition pulse side of the coil. Do not make any kind of connection to the HT leads or the spark plugs, this voltage is highly destructive

So my guess is to splice both the skinny black, and green tach lead with the "eye" terminal directly to the frame ground in the picture below. And my gut says the red should splice into the CDI line right there.

The coil installation schematic is in the lower right of this page from the manual. When I first read this, it sounded like I should patch the red tach lead into the green/ground lead of the coil because it has a (-) insignia at the terminal on the coil...but that just doesn't make any sense to me!

The bike's wiring diagram is fairly simple as far as these things go.

Below is a table of the various connections to the meter's body. The 10 element array is the one I'm concerned with.

Aside from the +/- leads coming from the tach sensor at the coil which we went over at the beginning, there are 3 other leads attaching here that I need to safely incorporate into the bike's harness somehow:

  • Ground was easy: I just spliced it into the same ground line used for my front turn signals.
  • Red "+12 Volts Battery" lead. It has an inline fuse. I had originally spliced it into the red battery line by the ignition switch, but that made no sense because the tach's LCD lit up as soon as I connected it. Perhaps I'm supposed to use something called a "relay" to mitigate this, but I see no mention of doing so with the tach installation instructions.
  • There is another red lead with a label on it: "lights on" presumably having something to do with...lights.

Curiously, I tried connecting the "+12 Volts Battery" line to the brown line in my bike's wiring harness, thinking it the tach could use the same line that my tail light uses (which switches on with my ignition key). THAT seems to work okay in that the tach powers on only when the ignition is turned on, no idea if I'm overloading my circuit insodoing...presumably the tach doesn't draw that much power tho ???

Oh well, thanks for reading through this for me. If you have any ideas I'd love to hear them. I look at the map on the upper right corner of this window tracking the visitors and wonder what you all are up to?


  1. Adam, if it is more convenient to tap into the ignition switch you might try the "other side" of the switch - not the "goes into" or "RED" side but the wire that gets the power when the switch is thrown (black). Looks like this black wire enables some lights and the rectifier as well as the amp hungry horn (do you have one?).

    Maybe the "lights on" wire can go with the blue wire on the headlight... Is there a rule in CA to drive with the light on - probably- so this, I guess, is an indication that yer head light is "ON" and may not be a critical piece of info for the operator but maybe it's a legal issue.

    I like the wiring bundling workmanship and especially the side panels. This project is coming out quite well. Your tach connections to the coil seem okay. I agree with your choices. We're anxious to see how this setup functions.

    I'm guessing you have no provisions to know what gear you've got. I mean, is there a legacy sending unit on the engine for the new TAC to interface with and then illuminate in what gear the bike has selected? With a little experience this data can often be judged by the bike velocity and the engine RPMs. I'm sure you know this technique but not enough time on this particular motorcycle yet.

    I haven't heard about the rear sprocket attach lore recently. How is that part of the story and the 8mm CSK fasteners that might want a certain grip length...? Did you fit a new rear sprocket?

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  3. Aha, the black line...surely that'll do.

    CA regs say the lights are supposed to be on all the time. For this bike, they go on only when the engine is running. Only indicator and signal stuff draws from the batt directly. It's just a 3Amp 12 V thing, so not much there.

    There are some instructions for using the shift lights as indicators in the manual. I have neutral only (green). The other two: high beam, and blinker. Blinker is important for me b/c i can't readily see if the signalis are blinking otherwise.

    I'll attempt this config right now and report back.

    PS: sprocket bolts came yes. They are the right length but are threaded all the way so not optimal. They'll do in a pinch, tho...

  4. I think you have the right idea following the schematic in the bottom right of the one diagram. In said diagram, there is a coil being powered on one terminal by 12 volt, and the other side is presumably the "pulse" side, throwing a grounding switch, causing the magnetic field inside the coil to collapse in on itself, creating high voltage which exits via the spark plug wire. Both the 12v supply and the grounding ("pulse side") wire appear in the XL600 schematic to be coming from the CDI unit. The CDI unit gets a signal from the crank position sensor, telling it to fire the coil at top dead center, and advancing spark based on how high the rpms are (adjusting for flame speed) and limiting the rpms to prevent them from going too high, saving you from valve damage due to valve "float" where the springs can not close the valves fast enough, usually this will hapen at extreme rpms.

    Anywway, the point is that just because there is a "-" symbol on the coil, doesn't mean that is a ground wire going to the frame. It just means that is the side that the coil's energy travels to ground through, the "switch" coming from the CDI, that closes every time there is a revolution of the engine (spark). So I think it will work if you connect the other two wires as shown, to ground, and then connect the red to the "pulse side" wire of the coil. There are only 2 small coil wires, and I bet it's the green one.

  5. cmgduce@yahoo.comMarch 4, 2010 at 5:40 AM

    I just stumbled across this blog and all I can say is WOW ...You are very talented, I love the fiberglass work especially the tank and "airbox". I have a GSXR 750 and Honda Trx 250r quad, this bike your building is killer ! !

  6. thank you there cmduce - it was a lot of work but i'm happy tooling around the local hills with this creation.