wud it make much difference if the co pot was disconnected while car was ticking over,also the plug has 3 wires on it i presume 1 is the earth but the other 2 wires both hav voltage running through them when the plug is disconnected,is this correct as i wud hav thought that only 1 wire should hav voltage running through it then when you connect the plug then voltage wud run through the other wire aswell

 

anybody

 

Yes it will make a difference being unplugged.

Its wired in series with the TPS so you may well get readings on a couple of the wires, its acting as a potential divider so needs a power supply across it.