Vinnie R. did a great write-up on a ST4s fan over ride switch installation a while back:
Fan Relay bypass question
I followed suit, since I didn't really like LT's set-up. The switch I used was a bit more robust than Vinnie's, I believe, but also obtained from Radio Shack. I installed it on the right hand side, and set a heat-shrink boot over the switch, after filling it with dialectric grease, so as to be reasonably water resistant. Very happy with the result.
I've attached three jpegs, first with the switch I installed vs. the one Vinnie used (according to the part number he gave). Second the full switch system prepared for installation, complete with fuse, and finally the switch installed on my right hand bracket for the brake reservoir. After that, I put the heat-shrink boot over it, with the grease, but somehow don't have a picture of the final product. This spring, I'll redo my electrics and put in one of the Centech AP-2 fuse panels, so that my air horn, heated gear, GPS and other stuff can be handled more elegantly.
Oh, and it works well with the CycleCat risers I installed, just some minor fitment modifications with the reservoir. Both mods highly recommended.
Ron