Mr. Shark,
If by "macro", you mean extension tubes + a normal lens or a Nikonos Close-up Kit, then aiming the strobe should be no problem: you are just pointing it right at the framer, right?
Normally, then you
(1) set the ISO setting one ISO number higher than the actual ISO,
(2) Close the aperature all the way,
(3) set the shutter for 1/60 sec.,
(4) set the focus on infinity,
(5) set the 105 on TTL,
(6) aim and shoot.
Immediately after taking the photograph, look at the full-power light: if it is flashing, open the aperature one stop. If your current problem is photos that are too dark (underexposed), this will solve the problem.
If your current problem is photos that are too light (overexposed), then you are probably not stopping the lens down all the way. Since the 105 is so powerful and the distance is so small, it is very important to stop the lens all the way down as the starting point for macro.
One more item: if you are using the 80mm UW Nikkor, do get a different lens, preferably the 28mm or 20mm. The 80mm UW Nikkor is almost impossible to use. The depth of field is so shallow, that focusing it requires extreme care. Very, very few photographers have successfully used it U/W.
Scorpionfish