Yell/blk(or what ever common colour on injectors u have is "+",ie 12V,& all 4 wires are joined at one of the shock tower engine plugs,& then a single wire from the main relay supplies this joint with 12V.

The other 4 wires go straight back to ecu & are "-",ie 0V,The ecu connects all these 4 wires to ground in turn to fire the injectors,so u will just want to test these wires are continuous,ie unbroken.Test as i previously described or use your new multimeter set on ohms to see if they give a figure of between 0-1 ohms,when u touch the probes to both ends of the wire(get a long piece of spare wire to join at one end to do this simply,so u can form a loop)