It's happened to me and quite a few others. Everytime when the speedo/tach quit working and the SCT not powering on...it's been fuse #8. Just pull it and look at it. Fuse #8 controls that ODB port. It's pretty easy to tell when the fuse is blown.

 

That would be my bet for your problem. Something is incompatible when you plug in the Xcal and the current draw is too much; it is drawing off that same circuit that controls the dash and obd port. A bigger fuse may help in your situation - especially if it is the automatic top causing the problem since you can't turn it off, but I wouldn't think the top would do it because it shouldn't be drawing any power unless you are raising or lowering the top. Can you turn the cathode items off and see if that resolves your problem?

It took me several blown fuses before I realized that it never blew out when I turned my satellite receiver off, and after talking with Xcal tech support who asked if I had any aftermarket electronics.

 

I learned a long time ago even if the fuses don't look blown they still might function just not correctly. I had so many fuses blow I've replaced almost every fuse with one when it blows shows a light. Makes life so much easier.

I would go through the manual and swap the fuses you think would fix the problem. I've done it many times Start at fuse #8 like people suggest

 

Y'all are pretty much awesome. You diagnosed the problem without even ever seeing the car.

Fuse #8 was the culprit. Replaced the stock 10 AMp one with a 20 Amp one. Hopefully, that should solve the problem.

I bet the whole "automatic top" thing might have been enough to push it over the edge.

 

i love how much information is on these forums.