Wiring elec fans with OEM thermo - s14

[nissan_s14]

Hey all,

Decided to let the OEM thermostat control one of my 12'' FAL's. Took the electric fan plug and hacked it off, exposing the wires...has 4 wires: brown/white stripe & black and white/red stripe & black. I assumed the black was ground and the other color was power (read somewhere white/red is high temp and brwn/white is low temp). Hooked it up to my FAL and waited for the car to overheat. After some time, the temp gauge rose to 3/4 the level of the temp gauge, but still no fan switched on. Got skurred :pface and turned on my manual switch (for the other fan) to cool it down.

Did I wire it right? Must I connect the ground wire from my fans to the chassis, instead of the plug?Have a s13 sr into a s14 chassis if it makes any difference.TIA