Pickup replacement

A friend has a mexican strat. The neck pickup is replaced by him. He says he put the wires the same, also tried it vice versa.
The following occurs: with the neck and middle pickup selected the sound is very thin, also the volume is getting down compared to the other possibilities.
In all other switches the sound is OK. The neck pickup selected on it's own gives a good sound.
Is there someone who knows a little more about the electric in the electric guitar?

I'm not sure if this is the reason, but I remember reading either on this site or at http://www.guitarnuts.com (great site) that your pickups need to have the correct magnetic polarization in relation to each other. That is, it must be a North or South, depending on what the rest of your pickups are.

From what I remember, the pickup polarizations need to alternate, e.g. Neck = North, Middle = South, Bridge = North (or vice versa).

If you do a search on this site (maybe try "north") or lookup the guitarnuts site, you might find out some more info.

Again, I'm not sure if what I just said is the reason for your problems, but it doesn't hurt to do some research on it.

the Pickups don't have to have a polarization like that, it helps because if you have a n/s combonation, they will hum cancel, so that's why most 3 single coil (strat like) guitars come with a N/S/N or S/N/S pickup arrangement.