i have recently taken my rear wiper and motor out and strapped up the connections in the boot lid.

now i was wondering, if i wanted to power something inside my vehicle, for example interior neons, could i wire these to the connection for the rear wiper so that i could operate them off the wiper stalk??

i so how much power could i run from this switch?

any ideas appreciated

The first thing to do is to connect a test light across the terminals and see if it stays lit up constantly. It may be, if the rear wiper is intermittant, that power will go on and off.
If there is a constant power feed there is no reason why you should not use it, I do not know what wattage the rear wiper motor is rated at but would think the circuit was rated at least 7.5 amps, possibly more.
If it is 7.5 amps then you can put up to 90 watts of lighting on to the circuit.
Just one thing, do not look at the fuse value on the wiper circuit and assume that is the circuit rating, the fuse probably protects other components so the value will be high enough to cope when all of them are on together. Good luck