How about getting a digital voltmeter instead of using your lights for that role - there like $10
a 40 Farad cap is just silly, your far better off with one or two small caps. Best solution add a good second battery ($120 - $160) add a cap to that along with the ALT and you should be good to go for any musical situation. Sweeps and other test tones on the other hand may still cause voltage spikes in the wrong direction. Adding a second battery is the easiest thing in the world if you already have a system installed. Should be like $20-30 in parts (not including battery) to install.
16V can be obtained by adjustable voltage regulator on your ALT. Unless you have a very good knowledge of the car's electrical system, i would not get one.
Caps in your amp help steady the voltage to your amp's power supply, they soften the spikes so that the amp has a more regulated (ie less fluctuations) input voltage. A larger cap outside will assist in this as well. This will keep the power supply operating more efficiently and in turn run the amp cooler. In theory this leads to a cleaner output as well. Some folks dont understand that and claim a cap is a burden - how something that does not consume or cause loss, is a burden is beyond me...... those people dont quite get the whole picture.
95 Contour SE '01 3L 
