You can measure the resistance between the ground point and the negative battery terminal. You'll need to add some wire at the batter to extent the length, and that wire will add some resistance, but you will still have a good idea what you're working with.

 

Yup. You can measure the ohms of the wire first and then just subtract it from the total. Sometimes I wish my MM had Zero out feature but not my cheap model . Someday.....someday

 

Thansk gijoe and bugsplat for the suggestions,

I finally got some free time over the weekend and did your recommendation. I had some 14 gauge speaker wire that i peal and connected to an UNI-T UT61E AC/DC True RMS Digital Auto Ranging Multimeter, it measure 0.13 ohm, then i tied one of the ends of the wire to the negative of the batery and the other lead to the multimeter probe, the other probe into where the ground was, and the measurement was 0.13 ohm, so 0.13 - 0.13 = 0, so i would guess by this the ground is good, unless the multimeter is not sensible enough to measure the difference between both measurements.

 

Sounds good to me. If it were a bad ground you would have seen something above 0.2ohms. My car had ground issues to the trunk no mater where I grounded. 0.5+ was common in my car. Ending up running a dedicated 4-gauge line from the battery neg to the trunk and put all my gear off the same ground. If you got 0, or close to it, you should be sitting pretty.