tricky one....

On Class 156 DMUs on the bulkhead that seperates the cab from the saloon, there are two lights behind a glass window. One is normally lit Blue, the other is normally unlit.

What does these lights indicate, and what does the piece of equipment do?

Provincial wrote:On Class 156 DMMUs on the bulkhead that seperates the cab from the saloon, there are two lights behind a glass window. One is normally lit Blue, the other is normally unlit.

What does these lights indicate, and what does the piece of equipment do?

If you are meaning the cab it would be either the spare button, Start engine button or coupler button

No, I mean on the passenger side of the bulkhead - my question avoided the cab as I understand not everyone has been in one.

Also Engine, Coupler, and Spare arent located on the bulkhead nor are they illuminated.

The lights in question are located drivers side of the wall, in the passenger vestibule.

I'll assume no-one knows

They are the proving lights for the TCA (Track Circuit Actuator) Blue- Operating, Red - Failed.

The TCA aids lightweight trains to occupy track circuits by zapping 110v through the wheels if it doesnt detect the 7v of the track circuit. These were added after it became apparant that DMUs were vanishing from signalling panels, especially with dirty wheel treads.

If the TCA fails the train must be taken out of service at the next available location, subject to other rules being followed.

If you look under the leading bogie of a 156 between the wheels you can see the TCA