Classic/Antique Car Repair: Charging problems - lucas dynamo, good luck jack, field coil

Question
My son Peter's  Austin A60 passed its MOT today.  On the way back the red light came on so he changed the dynamo when he got home, shortly followed by the control box.



Nothing.  Red light still on at all revs.



I went to have a look and found out that the light went off when you closed the contacts in the control box but they would not stay closed, and when closed manually the dynamo seemed to be straining. When you remove the feed (D) wire from the control box the contacts can be closed and stay closed.



Any ideas?  There is no break in the field coil wire (f) but that is as far as I got by 11. 30 p.m. . Could it just be he changed one dead dynamo for another?  Or could there be a short in the feed (D)  wire?  All advice/opinions  welcome!

Many thanks

John D  

Answer
I don't know anything about your car, but the control box sounds like a cut out.  Those fail all the time.  You can close it by hand, but the coil will not pull enough to make the contact.  Bypass the control box and see if the gen puts out OK.  If so, you need a new control box.  You may be able to get one with a diode in it so there is no coil to pull down.  That's all I can suggest.
Good luck
jack