Nothing complicated; first we need to remove the plastic housing and the 4 sliding contacts; these are on top of the firebox. There are four wires with their contacts. Unsolder the wires from the phosphor bronze (?) contact strips, but first check and mark what they do &--8211; get the old roof and remove the cover inside to check the wires for the cab light; unsolder & mark those first, then do the same for the remaining pair that control the rear headlight. The wires for both the cab light and the rear headlight are extended with thin wire; separate the wires into the purpose, and mark each pair for reference. Strip the covering from the pair for the cab light and tin the wire; do the same for the extensions, and add some heat shrink tubing before soldering them together; slide and fix the heat shrink in position; the now extended wires can be fed down the slot that was left when the plastic housing was removed. Do the same (with longer wire for the extensions) as this set have further to go at the same time; when complete coil this pair up as we will return to them in due course. The cab light wires can be soldered together when the cab has been fitted, again add the shrink wrap tubing.