Might try crawling under the beast and finding the starter. There will be a heavy duty grounding strap to a gang grounding stud on the frame. Loosen that nut and retighten for a good ground. This happen to us in a CG in the middle of nowhere and the ground was the problem. When we got home, I took the wire ends apart, cleaned and reinstalled...we also didn't have power to the dash gauges.
I'd also check starter terminal ends, they could be loose as well...but be careful you don't ground your wrench while doing so.
EDIT: Yeah, what's already been said above.
Jan and Bob