My Son's TTR90 has no spark.  We have swapped all the electrical components over from his other TTR. All have check out good. The only electrical lead/harness that has not been swapped is the lead running into the crankcase.  Where do these leads run and can I open the cover to verify them or would the more likely solution be to check the external wires for a short. ACn they become disconnected internally and would this lead to no spark?

We have been trying to fix this problem for some time (which led to the purchase of the second TTR) and would like any advise you can offer.

Thanks

Update-

I believe it may be the stator or magneto.  Can I swapped these out fairly easily.  I know I need a pull tool.  Is this correct?

Check your kill button. Disconnect it.

I have disconnected and ruled this out as well...

Don't open the cover just yet ! It's probably your spark plug. If not, it's probably the spark coil or wire. If nothing then take an ohm meter and stick it in where the spark plug goes then to a ground. Then where the smaller wire hooks to the coil and then to ground. You should have a complete circuit at both.