Chinese Digital Speedo/Tach

[BenjaminJ]

I'm in the middle of a cafe project on a 1980 xs650. A few months back, I ordered a Chinese tachometer/speedometer setup. Some of you may have seen it around (link below). I've gotten the wiring almost completely sorted in spite of the useless directions. The only issue that I have is that I can't get the Tachometer to work, I've tried a few things, and looked around, and everyone keeps saying hook the signal wire up to the pulse generator. Maybe it's a regional thing, but I'm not sure what exactly is meant by that. Any ideas?


http://www.ebay.com/itm/Universal-M...ash=item3f7bb0b3ab:g:GoYAAOSww9xZC9Gr&vxp=mtr

 

[grizld1]

The pulse generator wire is the wire from the ignitor box to the coil.

 

[BenjaminJ]

@grizld1 The orange one on this diagram?
http://www.xs650.com/attachments/80_xs650g-png.22985/

 

[azman857]

I think it's red wire on the bike. I have an '80 SG and also have one of those chineess digital dash too that I'm gathering parts for.

 

[BenjaminJ]

@azman857 On mine the colours happen to match. There's an orange wire and a red/white running out of my ignition coil. A BMW forum posted this as a solution to the same issue: https://i37.servimg.com/u/f37/19/60/00/88/screen10.png

 

[grizld1]

Ben, you have two primary terminals on the ignition coil. One carries 12V switched power from the kill switch; it's R/W. You can't get an rpm reading from a constant 12V power source, eh? Connect the tach to the orange wire. One more thing. Cheap electronic tachs tend to spike unless they're connected to an igniter box that has a dedicated tachometer signal lead, which yours does not. If you get erratic readings on the tach, install a 1 megaohm resistor between the coil and the tach. If the reading is still erratic, install another resistor. BTW azman, in all OE XS650 wiring harnesses, from first to last, solid red is unswitched power from battery to main switch.

 

[TwoManyXS1Bs]

I wouldn't recommend that BMW solution, as applied to an XS's TCI orange wire. The TCI orange wire can see voltages exceeding 100v, the cap in that BMW diagram is only rated for 25v. Besides, it has the signal grounded after the cap, signal won't get thru...

 

[azman857]

I can be wrong/remember incorrectly. My bad.

 

[grizld1]

Ben, it might help you to think about what's happening with the ignition and how the tach gets a signal to read. The coil has two set of windings: the primary windings start and end with the external terminals. One terminal (+) is connected to constant 12V power. That's the R/W on your coil. The other (-) is the ground contact; that's your orange wire. The ground connection is opened and closed electronically by your igniter box. When the ground connection is broken, the magnetic field created by the primary windings collapses, a high voltage charge is induced in the secondary windings connected to the spark plug wires, the charge seeks ground through the spark plugs, and the fuel charge goes "boom," (if all other things happen as they should). The signal that your tach reads is the interruption of the ground connection by the igniter box. Don't get confused over this, just do the needful.

 

[BenjaminJ]

Perhaps my tach is broken, it didn't register at all when I had it hooked up to the orange. Thank you all for your help!