Transmission Wiring Damage
Another common failure, especially when removing/replacing the gearbox is damage to the cable loom. I had noticed the damage to my loom while moving the engine/transmission around the garage. There was at least one severed cable and a few more that were badly compressed which would lead to a failure late on. The first image shows the broken wire and if you look closely at the orange wires you can see a couple have been damaged too. I cut out the damaged area and inserted suitable replacement wires. The connections were solder jointed and then covered with heat shrink tubing to protect the joint. Finally I used some loom tape to protect the complete loom.