My Jag starts and runs perfect until it gets to the half-way mark on temp gauge. It starts the surging up and down at speeds over 45 up to 60 and stops around 70mph. The car is cherry other than this.

I have it at a repair shop and the guy tells me its the fuse box under the hood near the passenger headlamp. The car was running and now its not after his probing and diagnosis. The fuse box is just laying unattached under the hood.

Has anyone else ever heard of this fuse box causing this type of problem?

Thanks for any feedback. My first time posting so I hope I did it correctly.