Head light dipping operations and wiring

I have looked at the wiring diagrams for my MKIV and cannot find any information as to how the solenoids are wired up to effect dipping the headlights, I have two solenoids and I can make the rod inside them retract but not extend. is this correct do they extend and retract ? or am I looking at this incorrectly ? anybody got any wiring diagrams for the solenoid operation ?
thanks all

This is for 1948 rhd 2.5 and 3.5litre

dipping headlight wiring
14 blue is 12V neg through the dashboard switch and the H fuse in the fusebox.
7 red/black is 12V pos and makes a connection through the resistance to ground when the dipper switch on the steering wheel is on
9 yellow/blue is 12V neg and makes a connection to the right hand headlight when the dipper switch is off.

The solenoid is only off/on, extends only one way. The roller moves out, pushing the swivel, and the other end moves in, tripping the connections, when the power is applied.

Whereas the export 1948 2.5 and 3.5 l had double filament light bulbs

Thanks very much, I figured out the solenoid operation, I did not have any of the pins with the domed head with my solenoids so was unsure how the plunger came out to push the plate to dip the headlights, IE I had them mounted the wrong way so now I have mounted it the correct way and I am making some pins

Here’s a picture of the wiring diagram from an MG TA/TB manual. It shows more clearly the local circuitry for the solenoid.

Here is a very informative article on how these solenoids work from the Austin seven club in Cornwall

A good find, very useful.

Yes, but it’s interesting that the Austin article says the law was changed for the 1936 model year to require both headlights to stay on when dipped. My 1938 car still has one dipping and one going off.

Yes Rob, I notice that myself, probably just misinformation or guess work because my Rover P2 still had the one headlight going out when on dipped beam in 1939

My reading of the document is that up to 1936 models, you can retain the original one lamp on dip, but later models must be converted to the standard system. “For cars after 1936 a conversion is required…”. It’s referring to what you need to do for your post 1936 vehicle for modern times, and to not retain the original manufacturing standard.

Remember this refers to the rules for classics in the UK, you would need to check what’s acceptable in your country. Factory exports had the conventional two lamps on dip.

It may be a case of misunderstanding or misinformation somewhere about when the law was changed.
Allan Crouch mentions it in his book SS & Jaguar Cars on page 114, discussing the post-war Mark IV, RHD cars for the home market having the offside headlamp switch off when the near side dipped, since double dip headlamps were not yet a legal requirement in the UK.

Yes, I believe the law didn’t change until late '48 or early '49, based on the Mk V wiring diagrams being all dual dipping for all models. What the Austin article is stating is that if you own a post '36 vehicle, you need to remove the single dipping function and modify it to be conventional dual dipping.