Gwagensteve wrote:
Check the GV has a heavy earth to the chassis rail. Sierras, and I think Vitaras, don't have earths to their chassis at all.
They definitely do have a small earth wire from the battery -ve terminal to a screw on the firewall.
Doing as the OP proposes would be okay so long as this cable is replaced with something heavier. This wire is probably only 6mm2 or so. Replace it with some of that 25mm2 and you'll be okay. Don't forget to fuse that +ve cable somewhere close to it's source.