Ya something must be wonky, as even I am running a 105 amp alternator, about 2000 watts, no dimming.

If you have leftover cabling, ensure that each of the following is done:

Alternator to battery (pos).

I like to use one lonnnnnng cable for the ground, "bouncing" it off of several spots:
Battery to frame (neg).
Continue to engine block, preferrably the alt bracket (neg).
Continuing with same cable, hit a tranny bolt too. Then continue on to the rear (assuming your amps are in the trunk), hitting the frame once again near the rear. Then into your trunk, and yep again, bolt it right to the same bolt your amps are grounded too. If you have a rear battery, then hit that too.

If you're still running into problems, aquire a small alternator pulley. Mine is off a Ford 302, commonly found in late 80's early 90's Mustangs & T-Birds.

And if you're still having problems, get a rear battery.

 

How old is the battery? Perhaps the alternator is on it's way out? What is the ground situation in the back where the amps are? Are your gains cranked?

 

What kind of fuse and holder are you using?

 

If you have a meter, measure the ground return resistance, what is it?

 

what happens when you put on the vanity light?

 

What happens if you're doing 50k, left signal on, radio tuned to an fm freq. below 95.9, with the sun visors down?

 

Now, what happens if you repeat each test without any pants on?

 

While singing "livin la vida loca"?