Reverse tail light stays om.
 

Light stays on no matter what gear or if in neutral . I have just swaped the transmission. Can it be because I connected it wrong? I know there are 2 white and 2 black connectors on the top of the trannsmion. Does it matter witch one goes where, or is it fine as long as it goes black to black and white to white?

As long as you connected black to black and white to white you should be OK. Likely the reverse switch is broken.... if you disconnect the connector does the light go out?

Where is the switch?

on the transmission
I think it is the white set of connectors...but I may be wrong....

Ok I will check it romorrow