I have a 1988 Rx7 vert, I just installed a Nissan Quest electric fan and now my brand new battery died (a week old). The fan is wired to a 40amp relay and when I turn the key to accessory the fan comes on. I need to know why my battery keeps dying

 

You need to check for a draw. What circuit did you tap into for power? Charge the battery and unplug the fan and see if the draw is still present. Should be more more than a 50mA draw.

 

I made a relay thing, (I’m not very electrical) I have a separate fuse box for it.

 

Just like mazdaverx713b said. Disconnect the fan from the circuit and test for a drop. Someone feel free to correct me if im wrong, but I don't think the fan should come on when the key is turned to accessory. Unless you wired it straight through without a thermo switch.

 

The fan should be wired to run only when the engine reaches a certain temperature. Typically a fan switch is installed that kicks the fan on when the coolant reaches the temperature rating of the switch. I would not have the fan running constantly as it can actually overcool the engine which is not good.