1979 rear master cylinder

yeah i see what's happening. 
the tab can be easily bent back to sit more upright so that it will press into the switch vertically, to activate it.   
the problem i have is that the switch (9) that i have and  i bought as a replacement to the original which is now obsolete, needs to be pulled and not pushed, so as to  activate it.
so, here i am trying to work out the piece that's missing in this scenario, which works to activate in opposite force or fashion to the
tab....
so, the good news is that the mystery is over....
the bad newsis i have to look and find a proper switch to suit.

The brake switches which are pulled to energize the brake light are pulled by a retention spring with hook ends on both ends. The one end of the spring hooks into the hole on the end of the brake switch pin and the other end of the spring hooks onto an eyelet normally on the top side of the brake foot pedal.

yes that is the case with some of my other bikes.

i think in this case with the 1300, if i'm not mistaken, as i apply the foot brake the tab pushes up vertically to depress the push /on switch that is fixed into that void from the top....
what i have is the opposite which is a pull/on switch.

The mechanism does normally push up into the switch

I damaged my brake switch being too heavy handed taking it out. I have now replaced it with a banjo bolt switch which works brilliantly.

I think Zed Parts in UK also has some banjo washer brake switches.

thanks zed thirteen...i had typed in the part number 27010-1027 i found in the parts book, for this switch....i bought it and not knowing any better, thinking or assuming they sent me the correct part, i got something that works in the opposite..........done over again....anyway, yes....it should depress and now reluctant to buy another one, because they all look the same garbage from asia....no genuine ones left....so your idea sounds good. are you able to tell me where you got yours? is there a part number with it?

all good.....found this application now, on you tube.

Sorry, I can't find my order details for banjo switch. I just removed a banjo bolt and checked its thread diameter and pitch and ordered one of evil-bay