check gauges light

Hi all,
I have a 2001 cherokee, 4.0L, 4wd, with auto trany. the check gauges light has come on twice now for about 5 min each time then goes out. the first time it came on the voltmeter needle went to zero (far left) the second time it happened the needle went to 19 (far right). it doesn't seem to affect anything while driving, kow, but I don't know if it could. the dealer only said "there must be a short somewhere".

Thanks