uniserver said:

i would not put voltage to both terminals as that would never be done in a normal situation, as to why you think that would be ok kind of bothers me.

seems like you know just enough to be dangerous. 

in a normal situation , to that 4 pin connector, it would be Either or.  there would be 9 volts to the one pin... OR there would be lead acid battery voltage to the other... never voltage to both at the same time. as the 9 volt battery is only there to keep what is in ram for only long enough to change the main lead acid battery.

Click to expand...

Incorrect. Both connections are tied together at one point, they BOTH see EITHER 9V (when the microswitch lets loose), or main B voltages. the 9V battery is switched in and out of the circuit through the microswitch. Its switched in when the battery cover is removed. 

I should know, I reverse engineered these things and fixed a bajillion of them. 

However, what I cannot remember is if 1 pin goes from 6V to 9V, while the other goes to 0V when the microswitch hits. But when the main battery is in, and the cover is in place, both pins are 6V.