Hey thanks for the help in the past I have a question regarding the temperature sending unit.
We mated a 20V BT into a 1990 Corolla SR5 using a tweakd harness.

Engine turned over flawlessly.

However the temperature guage sweeps all the way to H within seconds.
We checked thermostat its free and clear
we changed temperature sending unit and it is still sweeping after a few seconds.

Is this a compatibility issue occuring becuase we retained the original cluster? I'm assuming that the sending unit is routed to the ecu and then the instrument cluster.

This seems to be one of the few issues we experienced. Going to forward Tweakd this issue.
We are beginning to believe there is a ground strap we may have neglected to anchor. Could this be the reason why the cluster is malfunctioning?
Thanks for the help and direction!

Coolant temperature is a very simple circuit. Its a single wire. if this is your only problem then start by removing the single wire connection from the sending unit, turn the key to on and observe the operation of the temp guage. Then have a friend put that single wire directly to ground while still observing the guage operation with the key on. If the circuit is connected correctly from the sending unit to the guage then you should see the full swing of the guage full cold to full hot. If this happens then wiring and guage is all ok. This will also tell you that you should install the sending unit for the guage not the engine. Use a new sending unit from the correct vehicle. The swaped in engine uses a different sending unit .