i was just sorting the last few things out on my car before booking it in for an mot. and now it looks like ive got a bit more work 2 do.

if i turn anything elecrical on the rear wiper goes.
i mean turn the heater blowers on, head lights, hazrads, either indicator, full beam. they all make the rear wiper go.
the only things that dont is the front wipers and the side lights.

the correct switch that is ment for the rear wiper also turns it on and off as i should.
i checked the switched side of that switch with the other stuff turned on and there was nothing on it so it dosnt look like its being back fed through the cable.

any ideas what could be causing this?