I was asked recently to replace the 5 way selector switch on a friends strat which I did. However the tone controls only seem to have a noticeable effect when 'between' pickups not when middle or neck are selected on their own. It was like this before I got my hands on it so you can't blame my handiwork! Any ideas?

Welcome!

Based on my interpretation of your post, apparently you simply went, "shot for shot" off the wiring of the old switch, never verifying it to be correct for the electronics to function properly with the new switch. Is this correct?

Premising I'm correct, I suggest you look at a Stratocaster wiring diagram while verifying your work and while you're at it, the entire guitar's wiring and make whatever changes that are necessary.

As to who is to blame, no one makes mistakes here. We only make, "happy accidents"!!

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You dig?

+1 on what Martian said. This might help for a standard diagram :





Good luck!

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Actually I couldn't just transpose the wires as the original switch was 'inline' and the new one is a 'DM-50' from japan. I've checked the wiring and can't see anything wrong, the pickups are selected in the right order and the tone works when 'blended' just not individually. I'll have another look.