Thanks Dave for your idea's and thoughts. I'll save the info for if/when I have another go at them. if it is the common negative thing, that is a problem as most of my boats use separate batteries for lights, smoke sound etc. compared to the main drive which powers the receiver. One of the guys in my club took one away with the vague instructions and tried all permutations. I then looked at another and as far as I could tell set up a system on the bench (Hobbyking wanted a video). Obviously nothing to see operate as no moving parts. They wanted me to video the other 3 also until I got annoyed and said forget it. They then refunded. For now I'll stick with servo's and micro switches, at least I can see them work! 😀
Thanks

HI Derek
I have made my own electronic switches but have not tried the Turnigy.
Looking on the website, many say you need to have a common ground connection between the Rx and the switch (ie both negative leads common).
Looking at the unit both wire are red with no polarity marked. This suggests a relay but its very small to cater for 30v at 10amp. if it is a MOSFET of some kind this would need to be connected with the correct polarity and this is not shown on the unit.
The site says you should use a switched channel which suggests the unit detects when the pulse from the Rx goes from min (0.8ms) to max (1.2ms). On a stick neutral would be 1ms so moving the stick would give just 0.2ms variation which may not be sufficient to change the switch, especially if your trim has reduced the variation even less.
The version I built worked fine until I upgraded my equipment to 40Mz. The problem I had was because the pulse voltage was much lower on the newer equipment. Easily solved but I doubt if this would be a problem now.
I don't have the manual but it appears there are two jumper plugs which allow for on; off; either or last position. Apart from the either (default) condition I suspect this may give unpredictable results.
As you have your money back perhaps a friend with electronics experience could open one up and see what's the problem?
Dave