Been reading various threads on ES about this (there seem to be many references dotted all over the place). Now I have a bit better understanding what I'm actually doing. A few points I'm still puzzled by tho'. As a reminder my brakes are Shimano XT hydraulic disc ones with a reservoir attached to the combined brake/gear shifter levers. 1) Where to site the switch The only photo of these switches actually installed is here : Endless-sphere.com • View topic - Magura brake pressure switch These are approx vertical and there's nowhere else other than on the section running from handlebar end to front fork you could get them like that. I'd not have picked that spot to put them given a choice tbh - the switch is quite heavy and likely to cause the cable to shake there and so I would probably have gone for somewhere it could be secured to the frame with a bit of protection underneath to prevent frame rub. Also means I need to allow an appropriate length of cable when fitting the connector for a longer run to the controller. The installation instructions say this which as above I find ambiguous : Another point mentioned on ES is that someone said the switch failed when they installed it too close to handlebars and inserted a 5" extension to take it further away from them involving re-bleeding system etc. So does this all mean that the fluid should run air to ground through the switch for proper operation rather than left to right (or vv) through a horizontal orientation ? I kind of thought in a sealed system it shouldn't matter but others report so many issues getting this to work right I'd like to get it right first time if I can. 2. Mineral oil I have got a 50ml bottle of Magura Royal Blood as it is quite clear the switch won't work with DOT4 oil and I'll knobble a £30 piece of kit if I use it. Don't know what type of hydraulic fluid is in my system at the moment but let's say it could easily be DOT4 (bought the bike off someone else). Question then is - for this type of system with a reservoir do I need to bleed the whole thing dry before installing and won't there still probs be traces of old fluid left ? Is there any way to flush the system and remove it all without replacing the brake cable itself ? Still leaves the built-in reservoir to think about. If I have to flush several times then I'm going to need more fluid ordering in for when I get back next week . Not that easy to get these switches (most German suppliers are on 14-day stock procurement lead times or you pay your 30-odd Euros to e-bike easy again and wait a week if you mess up) .. and then you have to mod the new one on arrival all over again. Proper planning before attempting install worthwhile on this one methinks !