.. How to fix the fuse

I think fuses are usually in maintenance hatches.

There is another maintenance hatch in the Viaduct (right from the Tunnel).

Use a tool to open it. ( Maintenance hatches can be opened with a Wrench. )

A wrench? Good.

Open the Maintenance hatch at the Viaduct with the Wrench and grab the working fuse. It fits to the maintenance box next to the Crane.