If no current, Fuseable link OK with key off, then the ammeter, constant power circuits and alternator output circuits are not causing the problem.

Check in the ACC (accessory) position, and if no problems, then the problem is likely in the engine wiring harness. If the fuse blows in the ACC position, issue is in the Accessory interior wiring, check ignition switch to fuse block.

If problem only in RUN position, check connections at alternator, regulator, ballast resistor, coil, electric choke, any other item powered off the engine run circuit