Gauge Spiking

What would cause the voltage gauge to spike? It happens at random, almost everytime I drive now. Alot of the time when it jumps, it will stay that way until I turn off the rig. Other times it will drop back down to normal at random. But will usually shoot right back up again. Thoughts?

'99 XJ, 4 oh.

could be as simple as loose battery clamps/wires. or could be more complicated, beyond what I know.
or could be the gauge has bad ground, or loose wires to it... few dif possibilities.

edit: this thread found little further down the page.
http://naxja.org/forum/showthread.php?t=954873

Had the same thing happen on my 2000 xj. Clean the battery terminals if they have a bunch of green and white corrosion on them. If they are really bad, I would replace the leads as well. Then, check the grounds in the engine bay. I had one that had rusted through and was making intermittent contact. I ended up with a new battery, new leads, and had to move a ground. Haven't had a problem since. Good luck.

I doubt those are the issues. I have a Optima Red Top and Jeepers Creepers HD cables, only about 3 years on both. No corrosion, everything is clamped down tight. Ground to the block and fender are good as well.

Any other thoughts?

alot of threads like this, no one ever posts solutions. i have same problem any advice

this is an old thread, but since you asked, my friend finally got this fixed on his 97. He had random spikes, headlights and gauge cluster would get brighter than go back to normal. He was seeing a 19v spike at times.

replaced battery with a red top, cables with welding gauge stuff, grounds replaced with thicker ones. Got a new computer, replaced the batt temp sensor under the batt. cleaned all his connections.

what finally fixed it? On the advice of someone on here and from our boss at advance, he had gone through and in every electrical connector he had packed the connectors full of dielectric grease. He went through and cleaned them all out again with rubbing alcohol. Left a THIN film on the male ends, just a dab, took all the excess out. Problem solved, has not had the problem since.