05 Caravan, blinking, sweeping gauges, no start

Working on my sisters van.
Ive read about this common problem with caravans but there is one symptom I haven't read about.
Randomly the dash lights will start to blink on and off and the gauges will sweep back and forth, sometimes is just the instrument cluster sometimes the entire dash. The problem I haven't heard talked about is once in a while when the van is warmed up and you make a stop and turn the van off you can not restart it for a half hour. Put the key in turn the ignition and there is nothing only a faint fluttering of some relays but the door locks work, wait 5 minutes and try again and a few idiot lights come on dimly, wait another 5 min and the buzz will barely work and all the normal lights come on dimly, another 5 min and a little more power, this goes on for a half hour and then it will finally start.
The no start only happened to me once, same symptoms except after 10 minutes I turned the key on, left it on, I released the hood so i could go jiggle some stuff and as soon as I opened the drivers door to get out all power returned.
besides chasing down ground issues I'm hoping this might help the community narrow this down me.

Your input is greatly appreciated,

Instead of "jiggling" wires. Maybe inspect all the battery cables, clean(no corrosion) tight, etc. How old is the battery? Sounds like poor connections or voltage drop with bad wires.

I would head towards the IPM. Remove it, inspect the connections on the bottom for corrosion or other damage. Disassemble it and verify there's no corrosion on the internal circuit board. If all looks good there inspect wire harnesses under the battery for battery acid damage. If that looks good you may need a new BCM.

Well is been almost two months since I fixed the problem and it hasn't returned.
What I did was piggyback a ground from the battery negative post to the frame, chassis and fuse block, I also pulled all the connectors off the back of the fuse block under hood and found a few that had badly corroded terminals mostly on the spade terminals. I sanded all the male corroded terminals on the back of the fuse block and pulled the corresponding female terminal out of the connectors and sanded those as well.
Put everything back together and haven't had an issue since.

Nice work. Thanks for coming back with the fix.

Just curious. Have you tried disconnecting your added ground to see if it all works without it. It's sure not hurting anything though.