Well my lights dim when the idle goes low or when I put a heavy load on it but the main thing I notice is my dash lights and marker lights come on when I hit the breaks.

 

What is the year and model of your vehicle?
Lights dimming when a load is put on the electrical system is normal if the truck is only at an idle. If the RPM's are above idle you might see a slight dim before the alternator compensates for the extra load on the charging system.
As far as the dash and marker lights coming on when you hit the brakes, it sounds like you have a bad ground. Do these lights work properly when you turn on the head light switch? What happens to them if you then touch the brakes then? Are the brake lights working properly? Does their operation change if the dash/marker lights are on? For example are they as bright as normal, do they dim, etc. You have to look at all possible scenarios as you are try to pinpoint the problem and ultimately answer two questions. What should I see? and What am I actually seeing?