Combine soy sauce, Merlot, garlic, oregano, rosemary and pepper in a deep bowl.
Add lamb and turn to coat with marinade.
Cover and chill at least 6 hours or up to 1 day, turning meat over several times.
Remove lamb from marinade, reserving marinade for basting.
Rotate the lamb on the spit rods for 1 hour 15 to 1 hour 30 minutes or until the internal temperature reaches 135 to 140 degrees for medium on the instant thermometer, basting several times during the last 10 minutes.
Untie, slice and serve.