Step 1: Take part 1 and glue it to the bottom of the hull of the Sdkfz 250/1 as can be seen on the image. Then take part 2 and wrap around it the thickest of the two metal wires provided as shown on the image. Best is to do this by using a pair of fine tweezers. Once you have done this cut out part 3 and dry fit it together with part 2 in the hull interior as to be sure of their correct place. Use the images below as a guide.
TT002: Sd.Kfz. 250/3 Neue Art  - 1/72 Scale
Step 2: build the remainder of the interior of the 250/3 with the parts of the 250/1 interior. Use the image beside as reference, part details are on the plan of the 250/1
Step 3: To build the antenna and mount, glue part 4 to the upper hull of the 250 as shown on the image. Next attach part 22 from the 250/1 kit to part 4(see image for position).  Now take part 7 and connect it with part 8 (the length of plastic rod). Now take the remaining thin metal rod and cut off 6 lenghts of 7mm each. 5 of these should very carefully be connected with the upper half of part 7 as shown on the image. The 6th piece of metal rod should be mounted vertically on top of part 7. The whole assembly should then carefully be fitted to the antenna fitting on the hull which was made at the beginning of this step.
Besides the parts listed there are also two metal rods provided which are not shown on the image.
Now continue to proceed with the rest of the interior and kit according to the plan of the 250/1. Parts not to be used are 12, 19, 21 and 33. After completing the kit, continue with the final construction of the antenna.