The lever in the first (top) image is for the AWS warning system. You flip that lever to the up position and this will activate the buzzer/horn to alert you to signals etc when you go over one of the ramps between the track approaching signals or speed restrictions. The second image is for use when you are hauling another train (the class 375 electrostar in the case of TSW3). It verifies that there is a link between your locomotive brake controls and the brake controls of the hauled train behind. When running the class 37 only, this unit will not light up.
I have another question: in the first picture, the control lever was pulled down and the driver's cab was replaced and the train brake was operated. After replacing the original driver's cab and pushing it up, a strange thing happened - the train brake could not be released in any case, until the lever in the first picture was pulled down again before successfully releasing the brake. What is this?
It's a safety feature. When that lever is in the up position, the other lever to the left of that one must be also in the up position. This signifies that you are in the active cab. If you have to change cab ends, make sure the levers are down in the cab you are leaving and then when you change cabs, make sure the levers in the cab you are driving from are in the up position.
Thank you for your answer. I would also like to ask you one final question: What device is the ECU on the 37 locomotive? Or what is its full name?
The ECU is the device that interfaces between the 37's air brakes and the EMU's electropneumatic (EP) brakes. DMUs and EMUs fitted with the "Westcode" three-step EP brake do not have a conventional brake pipe, only an MR pipe, with the brakes being controlled by a continuity wire and three code wires on the "energise to release" principle. I don't think we need to know the ECU's full, unabbreviated name to understand what it does, nor even to have a very broad understanding of how it does so. The ECU, and the indicator panel that light is part of, are a special addition to the few 37s fitted with the Scharfenberg auto-couplers for direct coupling to the EMU; the other option is the use of "barrier wagons" with a normal coupling at one end and a Scharfenberg at the other. In just about the same way, the remote control handset for the RHTT wagons is provided only in the locomotives commonly used to propel them - though in that case, the modification to the actual locomotive is merely a rack to securely hold the handset.
ECU usually stands for Electronic Control Unit - that would fit with Taihennami's description of what it is and does.
