Thevenin equivalent...
Find Rth: flip the left switch to short the voltage source and close the middle ohmmeter switch to measure resistance. Leave the far right switch open.
Find Eth: Flip the left switch to the voltage source and open the middle switch. Eth is across the voltage meter. Leave right switch open.
To see the effect on the 1k load resistor, close it's switch on the far right, turn the left switch to the voltage source, and open the ohmmeter switch.
Thevenin equivalent circuit is drawn lower right.
