The Merlin trigger the camera by closing an opto-coupler: it acts more or less like a relay, so does not provide any voltage.
As I understand, the Merlin does not fire your Olympus? Try to remove the jack from the Merlin, and make a short circuit on its contacts: this should trigger the camera. If it works, then try to revert the wires in the jack. The opto-coupler can only drive the current in one direction, and your Olympus is maybe reverted.
Canon 20D + 17-40/f4 L USM + 70-200/f4 L USM + 50/f1.4 USM Merlin/Orion panohead + Papywizard on Nokia N800 and HP TC-1100