After a lot of head scratching I got the new RX18 working with the old style wiring that I had installed in the Tiger. In short you cannot just swap the new board for the old one, the T90 has a new 8 pin connector on the upper hull that crosses a few of the circuits so that the new tx operates the correct functions on the tank.
If you want to install a new RX18 in an old tank, then the connections for the 8 pin are as follows:
Old:
New:
Doing a complete rewire on the scrap Tiger, not using any hull socket, everything is hard wired as this was a quick and cheap job, I had to change it to:
1 & 2 = elevation
3 & 4 = rotation
5 = empty
6, 7 & 8 = lights and machine gun.
I now have the tank running as it should, everything is on the correct stick, the main gun works off press right button and stick up, machine gun is on left button.
Here's a quick video: