2002 international 9200i fusebox layout

The fuse/breaker and relay layout isn't the same truck to truck, but the common circuits like these should be. Trailer Marker and ID lights breaker/fuse is F3-A, 20 amp. Trailer Tail is F3-C, 30 amp. The way the breakers are laid out with F3-C for example, the "3" is the third column left to right. The "C" is the third row down. There is also trailer tail and trailer marker relays at the bottom. Ignore the vertical row of relays at the sides, and just count the bottom row left to right, 8 and 9 are your trailer marker and trailer tail relays. One of those could be bad too. In the bottom row, the 7th relay is for your electric horn. You could remove that one and swap with the trailer ones to see if the lights work. You should be using a test light and checking for power at your trailer cord for power, if no power, remove the cord from the socket on your truck and check for power at the socket. This socket and the cord would be the weaker spots.