MCU to switch single coil latching relay not working (attempting array with common gnd)
As I think you understand, for this model of the relay there is only one coil and set and reset are carried out by polarity reversal. This is indicated on the schematic symbol.



Figure 1. Coil polarity for set and reset operation.

The problem is with the ULN2003. 



Figure 2. The ULN2003 inverter and a detail of one output stage.

Notice that this is an open-collector transistor output stage. It can only pull low (sink) and cannot source (supply) current.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 3. (a) What you created (in top schematic). (b) What you need - H-bridge.

You need a little redesign. A simple H-bridge would do the trick. 

I don't know which coil voltage you are using but it may be possible to drive the relay coils directly from the micro-controller. Calculate the current required from the coil specifications on page 8 of the datasheet. Then compare this to the maximum source and sink currents of the micro-controller. Watch the chip total current too. You might be constrained to energising one coil at a time.









simulate this circuit

Figure 3. Snubbing options. Option (b) integrates the four diodes into a bridge rectifier saving some PCB space and soldering.