New tacho kills the engine on low revs

Hi!
Got a '85 GPz750.
Bought a new tacho from eBay and seems there could be a problem with a thing - As soon as i plug the wires, it kills the engin on low revs, but on high revs there is nothing happening and both cases nothing showing up on the gauge. As soon as i plug in my old original gauge, it starts showing what it supposed to. Wiring should be ok, as colors are the same.

Could the new tacho be damaged or rather this thing won't work on my bike?

Thanks

Have a look on the recent 'stock v dyna'' thread, a member here had problems with a non standard tacho, solved by changing to dyna coils.