"The other fuse" - you mean the two fuses in the box next to voltage regulator?
If so, then for the radio there is a wire going to that box from R connector in the ignition switch (the first stop of the ignition key as you turn it). It goes in the cable harness. It is red/green. You need to find it in the harness near the voltage regulator. Need to pull out its end and screw it in this fuse box. Then from this fuse box the new length of wire goes througgh the grommet in the firewall to the radio. It is then powered when you turn the key in the ignition to R position or Ignition position. At least for most cars it is done this way.
If you had optional power antenna, there was another wire in the harness next to the red/green, that you need to pull out of the harness and screw to the second fuse in the fuse box and also lead another length through the grommet in the firewall to power the antenna. This is a red wire, a bit thicker than the red/green. This wire has power at all times.
The set up above is addressing, I think, your question on having radio on/off with the ignition key. This is the "correct" way of wiring. If you have troubles with finding the red/green wire and you do not want to get behind the dash to lead it yourself, then the solution is to power radio from one of the points that have power after ignition key is turned (e.g. one of the fuses). But this is not original solution.
If you already have this red/green wire in the fuse box (so it feels from your post) then there should be another wire from this fuse box, through the fire wall - to the radio. You would just need to hook it to the radio.
