How to hook up a load cell to an Instrumentation amplifier correctly
What you have is probably two strain-gauges in each package forming a half-bridge.

The wire colours could mean anything so what you have to do is take a multimeter and measure the resistance. You should be able to figure out what you measure from this: -







simulate this circuit &ndash; Schematic created using CircuitLab

Between two of the three wires you should read a resistance that is twice as high as the resistance between the 3rd wire and either of the original wires. The wire in the middle (above circuit) is the input to your amplifier and the wires at the top and bottom is where you apply your excitation voltage or current.

As a start, two of the three-wire load-cells can be excited together and the individual outputs fed to an instrumentation amplifier but, there's one more thing; whatever colour are the excitation wires, make sure they are applied oppositely on one of the load-cells - this ensures that one output rises with load whilst the other one falls. If you don't do this you will not measure a signal.

That gets you two load-cells into one instrumentation amplifier and to get 4 load-cells either parallel them up or use another instro amp.