To find the Thevenin equivalent voltage ($V_{th}$) between points $a$ and $b$ in this circuit, let's analyze it step-by-step. Here's an overview of the components and sources in the circuit:

1. Voltage Source: 12V at the left side.
2. Resistors: There are resistors with values 2$\Omega$, 6$\Omega$, and 4$\Omega$.
3. Current Sources: There are two current sources: $i_1$ and $i_2$. The first one is unspecified, while the second is 2A in the middle branch.

Here are the steps to find $V_{th}$:

Step 1: Identify the Voltage Across $a$ and $b$

1. Use the superposition theorem or mesh/nodal analysis, considering each source separately to calculate the contributions to the voltage across $a$ and $b$.
2. Add these contributions to get the total $V_{th}$.

Would you like me to delve into superposition or use a specific method?