1993 Nissan Cefiro Electrical system gone dead

I relocated my battery to the trunk of my car a week ago using 2 power posts in the engine bay to connect 2 negative cables and positive cable as well as additional wiring which used to go to the positive post on the battery.
I ran the positive cable through the interior of the car all the way to the triunk to be connected to the battery. I also have another negative cable grounded to the body in the trunk that also goes to the battery.
The size of the cables are 2 gauge and the positve cable being the longest is about 20ft. The car worked fine for a week and when I tried starting it today all the electricals went dead. I checked the voltage on the battery and it read 12.4v.
I also checked the voltatge coming from the positive cable going to the engine bay on the powerpost by itself and it read the same. But when I checked the voltage on the positive cable while on the powerpost with the starter harness,
main harness and positive battery cable attached it just reads 1.3 volts. Can you give me some idea as to why I would have a break down in the eletricity?