Do you remember the realy old mats that had a tarton cover on them.
I serviced loads of dry cell systems over my time the one's with the end of line flag battery with a diode fitted to them, all well over 30 years old. It had a green lamp on the front that lit up when you pressed the test button if all was clear.
The whole house would be run in brown twin a + loop and a - loop in the same cable mats caused a shot and doors went on on of the loops.
F,in nightmare to find a fault.