CARBoy

I'm trying to determine what the evap Leak Detection Pump wires do in my 2004 base Miata. (I need to hookup the two evap wires from my LS2.) I understand what the pump does and have figured out where the 4 wires go, but I'm not sure what the 3 non-ground wires do. And why there aren't just two wires to run it...

BLK - Body ground. So this is obvious.
WHT/RED - Goes to terminal D of main relay. "Hot at all times" per schematics. Maybe just powers the pump?
YEL/BLK - Goes to PCM terminal 3K
RED/GRN - Goes to PCM terminal 4AH

The last two are the real unknowns. Perhaps they trigger the dash light or OBD code?

Thanks for any insights,
Jon

CARBoy

Answered elsewhere...

"There is more to the leak detection pump than you think. There are actually 3 parts to the pump assembly, the pump motor, a heater, and a solenoid valve. The WHT/RED wire is the power supply to all three and is only "hot" when the main relay is on. The Black wire is the heater ground. The YEL/BLK is the pump ground circuit which the PCM grounds when it decides to turn the pump on. The RED/GRN is the solenoid ground circuit which is also controlled by the PCM. The PCM monitors the voltage on the two wires going to it to determine if the circuits are good and will set codes if things don't look as they should."