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For all the temp-sensors I've ever worked on (that I can remember!), whether coolant, oil, trans, diff, etc, it was 1-wire... just jumper-ing the single lead to engine-ground (block, battery, ground-wire, etc) would drive the sensor to max-temp (infinite resistance?). On most of our Toyotas, the needle will jump to the max, when the single-wire sensor is jumper'ed to ground.
I completely agree if its a single wire.
Just straight ground it.
But it looks like the GS400 engine temp sensor has a 2 wire connector.
Only the OP can verify this.
Good news. I got her fixed! The new temp switch was bad. I also think it was a few other things that I read up on. The oil control valves were dirty so I cleaned those and re-installed. I also cleaned my mass air flow sensor and throttle body intake. Lastly I changed the thermostat. Ran the car to temp with the radiator cap of to bleed the system and voila! Car runs like a champ now. Thank you to everyone for your very insightful help!!!
Good news. I got her fixed! The new temp switch was bad. I also think it was a few other things that I read up on. The oil control valves were dirty so I cleaned those and re-installed. I also cleaned my mass air flow sensor and throttle body intake. Lastly I changed the thermostat. Ran the car to temp with the radiator cap of to bleed the system and voila! Car runs like a champ now. Thank you to everyone for your very insightful help!!!