lights dim when doors lock?

in my 1996 mazda protege, my lights dim because of my sound system. but the other day i noticed my dome light dims whenever i lock or unlock my doors from the electric door button. my battery has 450 cold cranking amps so i was thinkin about gettin an optima red top. i have upgraded the negative battery to ground wire of the big 3, but my alternator is so hard to get to i will probably not do alt. to batt. positive. what should i do?

Have you done a load test on the battery lately? You may simply have a bad battery.

i did a while ago because i got a new alternator, and it was just fine. but that was maybe 2 months ago. maybe i should go to autozone

Can't hurt, and can usually save a headache in the future.

I have an Optima Red Top, with a 200A alternator, 2F worth of cap in the trunk, and my dome light is LED. I still get dimming. My wife's brand new Fit, completely bone stock, and brand new off the showroom floor had the same thing occur from the day I drove it home. Even to this day, if the headlights are on, and we are driving down the street, if I bump my lock tab down, and all the rest of the locks go with it (which they do) even the headlights will dim a little bit, and the engine is RUNNING! I don't personally believe there is anything wrong with any part of your electrical system at all, including the battery. The door locks are solenoids, which are a VERY high inrush current, and this is (generally speaking) a normal situation, to see a little bit of a dimming.It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

o ok then. one more question: i upgraded the negative battery to chassis with 4awg wire and now my headlights are VERY dim. i did not remove the factory wiring and i did not sand the paint to bare medal under the bolt i attached it to. any idea why?

upgrade your big three if you havent