I have just come across this amazing site - http://dickthesignals.co.uk/home/about.html
. I have linked to a page of this in the past but I didn't realise just how much is here.
This is what he writes on the preamble page:
"During my career as a railway signal engineer I collected a vast number of technical documents which I know could be of use to those working on heritage lines or possibly parts of the national system where older types of signalling equipment are in use and modern standards may not exist.
This is not a comprehensive collection or an authoritative manual on how to carry out a given item of work - it is really the contents of my loft placed on the internet for you to use as you wish! It will hopefully be more use here than left gathering dust. I cannot guarantee how up to date or accurate this information is and you have the responsibility of using it correctly. I am still in the process of uploading information so you may have to wait for what you are looking for."
Once you have worked out how to use it, there is all manner of interesting and useful information particularly for those with an interest in S&T matters but also on signalling operations.
I don't know who Dick is - he may even be a subscriber here - but this is an extraordinary resource for both historical research and for more up-to-date matters and I for one am very grateful for the work he has expended to publish all this material. I also don't know when this site was created, whether it is a work in progress or a finished object but if you want an insight in some S&T technical matters or just a browse for a quick click on to something that looks interesting, it is well worth a visit.