I had a similar problem after buying my used XC. Right after I bought it the speedo would go up and down, sometimes staying at zero, sometimes staying pegged out. Turns out it was a short. I just happened to reach up under the front cowling on the left side and gently felt around, evidently moved some of the wires/connectors, and everything has worked fine since. Probably need to do some of the soldering mentioned to make sure all connections are secure. But you might try some gentle wire moving - the price was right !