Does the fuse blow immediately? Is the 10 Amp fuse at the end of one of the rows in the fuse box that keeps blowing. You need to start with a wiring diagram.
There are three 10 Amp fuses in total in the shift lock circuit. One supplies power to the brake light switch if it fails you also loose the brake lights. From the fuse I suspect is failing, a white/black wire runs to the shift lock control unit (under driver's side center of dash). The box you are looking for has 10 wires going to it. Pink, Blue/Black, Green/Red, Yellow, Blue, Black, Blue/Red, White Black, Blue/Red, and Green/Yellow. The black/white wire goes from the fuse box to the control unit to the shift lock solenoid. Try wiggling and shaking the harness to see if you can get the fuse to blow then look for that a short to ground in that area of the harness. It is likely the short is around the solenoid. If you had a wiring diagram from a workshop manual and start tracing the electrical circuit it should be relatively easy to find the short to ground.