I also used the ST205 fuse box. My reason was that the ST185 stock fuse box was having bad contacts in it and I wanted to have a fuse box without problems. Usually, it is easier to use the car's fuse box, but if you change it for a new one with even more relays than you need to, it leaves some place for expansion and it can't hurt. If you go that way, just make sure that you know what each relay does in both fuse boxes and what wire is used for what function. It is more complex to change the fuse box for the ST205 one but the pinout that I sent you is really a good help that you can count on. You just have to do the same job for the ST165 one. On that side, I can't help you, because I did it for my ST185 and don't know how ST165's are wired.