Soooo, I’ve noticed the pot on my old machine seems a little dirty, I bought one of these (http://bit.ly/1rvZYm1) a few months back but not sure how to wire it in. Can someone please enlighten me? Thanks 
From what I see on the pictures (can"t access ebay at work), 1 should go to 5V, 3 to Gnd and 2 to IN
Once wired, turn the laser switch off and use a voltmeter between IN and GND, if when you turn clockwise voltage goes up you’re good to go, if it goes down then Wire 3 to 5V and 1 to GND
For anyone else that may be interested on the stock k40 PSU wiring, pin1 white 5v, pin2 purple In, pin3 green Gnd.
So wish I did this mod months ago, setting power is so much more accurate and easier now. Thoroughly recommend anyone with a analog K40 to swap the pot out for one of these!
K40 have a lot of different PSU, and a lot of wiring color, yours will not be the same as mine for exemple 
Ah fair enough, thanks for your help by the way!
You’re welcome
MY Redsail came with a 10 turn pot, so much easier to get the exact power you want.
Yeah it’s crazy now thinking of the lines I had on the machine and multiple test fires to make sure the power was right. Now I just dial it in and it’s good to go. 
I fixed my setting problem by installing a digital voltmeter across the existing pot :).
@donkjr That is a great idea, I assume you turn your pot until it reaches the voltage that correlates to the desired power setting?
Yes, the design just wiring in a meter from amazon (was posted somewhere here along with K40 schematics). I make test cuts on various materials and write on those test materials the digital setting, speed etc. which I keep as a library item for reference.
@funinthefalls I posted the digital meter hack since i cant add a picture here. Disappointing that you can’t directly add from your Google photos to G+.