Help! 1998 Dodge Caravan electrical mystery.

I have a 1998 Dodge Grand Caravan Sport 3.3L that I've owned since new. It's been very good to me and has nearly 200K miles on it. My son has been driving it at college and it recently started having issues with starting and the radio cutting in and out. He brought it home to check out. I found the battery was fully charged and wouldn't put a draw on a battery charger. But the terminals were extremely corroded. I cleaned up the battery and terminals with water and baking soda, put a little dialectric grease on the terminals, and cinched it all down. It starts right up but all of a sudden I have no gauges, no park or headlights, and the electric locks don't work. The turn signals work and show on the dash, the parking brake light and other idiot lights work, but the tach, speedo, gas gauge and temp gauge all quit working, along with the lights and locks. I've checked all related fuses and they are fine. I can't even begin to imagine where these different functions would intersect. Can anybody offer any clues or advice?!?

ant remember the years this applied too . But there was a couple years they had BCM issues would cause weird electrical issues.

Unplug the BCM and see if functions return

Thanks for the suggestion. But I tried it and no luck.

I don't know if this applies to earlier years, but Gen IV Caravans (2001-07) had corrosion issues with the connections under the underhood fuse box. The Gen IV fuse box pivots so you can see underneath.

It's the BCM.

As in replace the BCM??

If it's the BCM will the OBD port show error codes? I think O'Reilly auto parts does a free OBD error check.

I would be looking for a bad, corroded, or missing ground between the battery and the body.

Did you remove the battery cables and cleaned the posts and terminals, or did you just chemically clean the posts? Chemically cleaning doesn't always get the job done, especially if they are really bad. I would also consider replacing the terminals on the cables or replacing the entire cable. A lot of problems on old stuff is fixed with good clean metal to metal battery connections, on both ends of the cables. Gene

Try unplugging the cluster.(reboot) Except for the headlights? You did say you have no headlights right. I would address that problem first. Do the headlight come on when you flash them with the turn signal stalk?

Thanks for the suggestions. I will try and check the grounds tomorrow. I checked for continuity, resistance, and voltage drop between the battery and the fuse/relay box under the hood and everything checked out fine. I physically cleaned the battery posts and terminals. I don't think the issue is at the battery, but a ground problem at the relay boxes sounds like a possibility.

Nope, they don't flash. I also found out the power mirrors don't work. But the power windows and the brake lights do work.

Try to unhook the battery again and turn the key on while its unhooked. I had the same thing happen with an 02 caravan, dash lights, speedo and tach quit, hooked battery back up, all was working again.

So, reconnect the battery with the key in the ON position?

I was not there personally to see it but back when my mom’s 2005 T&C 3.3 was just a few months old my father said he simply pressed the trip odometer reset button and suddenly lost all Dash lights and functions. The BCM was replaced at the dealership under warranty.

I have seen the driver’s side power window suddenly quit functioning,
then suddenly start working again weeks later.
When it quit I could see the a voltage drop when the down switch was depressed, indicating the motor had a locked rotor with not enough troque to break free.
During the time the power window was not working I now remember I put a pulse style desulphating charger on the battery for 48 hours, and cleaned connections, including the block ground terminal about two feet below the battery posts.

I will keep in mind that there may be “green death” on connections below the engine compartment fuse box.

In the relay/fuse box in the engine compartment, check the fuse labelled
I/O (input/output) if it's blown then replace. If it's not blown pull the fuse wait 10 seconds and reinstall.

We used to have a 2000 that started to weird things. There was corrosion in the harness below the battery from acid residue running down from the battery.

No, turn key on with battery not hooked up, gets any battery voltage stored in the vehicle to 0.

Buddy's did the same, tried a lot of things. One mechanic said to pound the dash with his fist, he did and it would work again. That tells me bad ground connections around cluster. He did replace cluster and is working fine now but the disconnecting could have been helpful too. How many times in older cars just wiggling the fuse cured issues.
Common practice on those 70s Dodge trucks with the fuse panel on top of the dash under the glove box door (spilled drink)

I would track down why you have no headlightsmost likely related to the other things wrong.

Another common issue in the late 90's minivans was the wiring bundle that ran next to the trans pan - the convolute was not wrapped in some areas and the sharp trans pan chaffed wires. Caused mostly power train issues but I believe there were some body electronics affected as well.

I had issues with my Durango and the wires pulling out of the ignition switch after years of operating the tilt wheel. Worth taking a look.

Allpar has a neat little write-up on this subject......
https://www.allpar.com/model/m/repairs/3G-cluster.html

So, the van sat for 2 days before I had a chance to work on it again today. And when I fired it up everything is working. To me that says I can rule out fuses or something like a broken wire. Probably can rule out relays, too.

This might have been the equivalent of the earlier suggestion to to turn the key on with the battery disconnected to remove residual voltage, but not sure.

I think a bad ground is still a possibility so I'm going to pull the relay/fuse box under the hood and check all the grounds and cables that I can see. But it could still be the BCM is bad and it temporarily "healed" itself. Time to get out the wrenches and go exploring.

Thanks for all the advice from everyone!

Took it all apart and nothing I can see looks corroded. Anyone have any thoughts on whether there would be any gain/advantage to running an extra ground from the battery to the engine and/or body?

Extra grounds never hurt.

If it happens again wiggle the ign key as I had ign switch problems with some. I also had some lose all the lights because they would set a code in the BCM for dash lites and as long as the code was in the BCM it would not let the lights function. If I cleared the code then everything worked. And I had some that I could not get the code to come back so I told the cust if it does it again bring it right back but they never came back. Only a few did that and many never set the code again. It would be a good idea if it happens again to check the codes in all the controllers to see if any have set. Good luck , Ron