MG Car Repair: MGB (Canadian Spec.) brake failure light

Question
My brake pressure failure switch on my 73B has failed itself and is leaking. I am wondering if I have to replace it since the interior brake pressure light has never worked in the 10 years I have owned the B. Can I just remove the old switch and install a plug?

Answer

MGB Brake failure unit   Hi Andre
The brake pressure failure unit is a very simple device.  It compares the pressures in the two independent circuits and if they are different, then it operates a switch that turns on a warning light.  However, if the unit fails due to worn out hydraulic seals, then brake fluid can leak out through the switch.  Sealing the switch hole will not fix the problem, because the two brake circuits would be joined together into a single circuit, which would be dangerous.

I attach the relevant page from the workshop manual.  You can see that it is very easy to take the unit apart and replace the seals.

The warning light has a manually operated switch.  The only function of the switch is to test that the bulb is working.  It does not test that the failure unit is working.

I recommend that you buy the correct parts from Moss Motors, strip and rebuild the pressure failure unit, and fit a new bulb in the test lamp.