Hey I'm getting the old headlight pulsing when I crank up the sound in the vehicle. I've replaced the stock battery with a deep cycle which hasn't helped. Also, when the bass amps running near full and i'm driving, I get a electrical burning smell through the air ducts.

What battery should I be using , and do I need to up-size the alternator as well?

That sounds like fun. What gauge power and earth wiring have you got for the amplifier?
How many W RMS is the amplifier rated for - to give an idea of it's power draw on the battery.

I believe that a common cause for this is insufficient quality on the earthing side.
You may need to improve the earth at the amp, battery or both.

Or if they are up to scratch, it could simply be that the current draw from the amp is too high.

Supposedly a big capacitor will help smooth the drain on the battery / alternator and let the amplifier get it's power when it wants it.
That's the theory behind "cap"s at least - I've had no experience with them other than seeing them used for purely cosmetic purposes :)

Thanks for that info Oggy. I did check all that stuff out (running 200A wire to the amps. Not getting much joy, so will to get ia pro onto it i think.

what is your gorund like and where is it grounded. oh and this should be in the audio section.
find a good solid earth point, that is a shortest possible distance to the amp. and what gauge wiring is it?
if your getting pulsing try bigger then 5 guage, IE towards 0