Necessary step for some shuttle valve switch bypass methods

I discovered that with some shuttle valve switch bypass methods in which the shuttle valve switch remains electrically connected to the hydraulic control block there is a polarity and if you have it backwards the lights come on right away! Here's a link to a brief video I made two years ago describing this necessary step or how to diagnose a problem.

OK, so let's continue here even though as you mentioned that : "... with some shuttle valve switch bypass methods in which the shuttle valve switch remains electrically connected to the hydraulic control block..." you might have a case but the gist of all this mod is to NOT LET THE SVS CONNECTED !!! if you want a job well done.

First of all the "bypass" shown in that video is wrong cos the guy splices into the circuit with the two additional wires which means that the faulty internal circuit is let in parallel with the mod and there were cases even on this forum when this kind of bypass didnt extinguish the 3 amigos but they went out after the wires were cut and prolonged maybe cos it was a current "leak" or short within the modulator which modified the overall resistance of the SVS circuit or the internal issue can behave differently one way than the other if one side has an electric "leakage". I can admit that if the SVS connector is not cut out then switching the "polarity" might help in some cases but it's not the correct way to fix that cos in time the internals can get worst then it's back to square one. So, being an engineer too(used to work with avionics long time ago) and after about 15 years of study on the D2's electronics with several mods done, i even dismantled a switch pack in small pieces i can bet my house that if the SVS pack is not faulty and the wires are cut and prolonged not spliced into them like in the video it's completely irrelevant which wire goes where, this is quite obvious from the scheme in that link with the "necessity of the mod" . To be more clear i cropped and edited the relevant part out of that WABCO file, consider the blue square as the SVS pack, the green and pink arrows being the additional wires so please explain technically as an engineer how that 4 resistor setup can behave differently one way or another if one wire is to the YG input to SLABS and other to earth while the modulator's internals are completely out of the scheme.(english is my third language so there can be misunderstandings only based on that not on the pure technical side of this discussion)

Good morning, you're right the circuit board is left in and becomes a parallel circuit once the two wires are tapped into the shuttle valve switch and I think you get what's going on. The proper way to fix it would be to change out the circuit board if it was sold separately but I'm guessing you would probably have to buy the entire hydraulic control block and then bleed it using a special procedure that would require buying a special tool. Doing that mod that way or any other mod is not the proper way of doing things, it's just the cheap quick way of getting back on the road not a long lasting, proper or permanent fix. That's why I made a point of saying and then reiterating In the following that I don't promote any bypass method. That video we looked at and both came to the same conclusion about has had over 100,000 views so there's going to be a lot of people having problems. I made my discovery and documented it in video format two years ago. It sounds like you understand that the procedure I came up with as a fix for certain shuttle valve bypass methods works, you just don't like the whole concept of not fixing things correctly and neither do I. To anybody else reading this if you doubt what you see in the video just read all the comments thanking me for coming up with this method. Also I apologize for the video being so brief; My thought at the time was: it's a simple test and or a simple procedure using a ohmmeter, I should just get to the point! Land Rover should've had a recall for this problem it's ridiculous! Mr. Sierrafery, Thank you for your input and for posting the schematic it is greatly appreciated!

You can buy the switches seperately, I converted a spare new switch and fitted that.

MJI said:

You can buy the switches seperately, I converted a spare new switch and fitted that.

Click to expand...

Thank you for your input, you are correct and good move! I did the same thing: Why reinstall the old switch when a new one was only about $20 US.