how to test for a good ground with a dmm

what do i set the dmm to and what do i connect both probes to

if you do a search, you will find other posts where this topic has been quite well discussed. If you want a quick answer, then here is how you do it. Set the meter to Ohms and connect any one probe (usually black one) to the ground such as any metal part of your car (assuming yoru car is -ve ground) Touch the red probe to the metal part you are testing for a good ground. If the meter shows almost zero ohms, (less than 1 ohm) it is good ground. The reason why it is not absolutely 0 is because your contacts between the probe and the metal part is not too good.    If you soldered your probe to the metal, you would see zero ohms. Also set the meter to the lowest ohms range you can to get a better reading. If you set the meter to a high ohms range, anything will show you a reading, even if you touch the probes with your hands!

my ground cable is getting hot and the copper wire is changing color on the inside of the insulation what would cause this the positive doesnt get hot at all

Sounds like not a solid ground or theres paint in between the ground and the body of  the car, or even not large enough ground wire, the amps pullin to much current

I would agree, it sounds like a bad ground but I am going to go with too small a ground wire. The ground wire should be the same size as the power wire. What amp is it hooked up to, what are the fuse sizes in the amp and what guage wire are you using.Top Secret, I can tell you but then my wife will kill me.

I always test for ground return resistance by taking one probe direct to the neg battery terminal and the other probe to the potential grounding location. This will show the resistance from the battery instead of between two points. Never touch the probes as it throws the reading off. If the probes do not reach, use an extension wire to lengthen the reach. A reading of under .05 ohm is what I usually shoot for.Top Secret, I can tell you but then my wife will kill me.

i am using an hifonics zeus viii amplifier 8 guage wire 100 amp fuse

Your power and ground wire should both be 4 gauge at the smallest, the 8 gauge is not large enough.Top Secret, I can tell you but then my wife will kill me.