I know this its dumb but I did it. I was boosting my 91 240sx with hicas, boosting meaning that I had no juice in my battery not turbo it, and I plug the wrong wire on the wrong battery pole. Now I run always at 285 km/h even if the car is not working. My dash lights wont open unless I give it up some gaz. Is their any fuse or something like that to prevent someting as dumb as that??
As for the problem, you may have done damage to the alternator or the battery, i’m not sure about if there is a fuse of any sort.
What does “run at 285km/h” mean? Does the car start/run? If lights are dim/dash lights on etc etc…chances are battery or alternator are toast unfortunately…
Give us more details. You may end up needing a mechanic to look at/test it…
If it was a fuse… you wouldn’t see any reading at all. You might have fried something fairly important, speed sensor or the display itself. Have a qualified mechanic look at the problems and see what else isn’t working because of the same problem… I doubt you broke only one thing. But if you did… you are very lucky.