Is there a charge controller between the battery and the solar panel?

There must be a charge controller in between or the battery will be destroyed.

edit; oh you mean house battery as in not in the vehicle. Disregard.

 

I think the 'house' battery' is indeed in the van, it's just for the 'camper' stuff. Likely charges from the same system as the under hood battery, while the engine is running. If it does, and there ISN'T an isolator, that could be the whole problem.

 

Yes, House battery is in the van just for the camper stuff. It did charge from the alternator through a relay that would only connect when the engine was running and did have an isolator. It would be isolated when the motor was off. But I've removed all of that hardware...

 

If the batteries are connected, and they aren't in perfectly equal condition, they will discharge each other. You need the isolator.

 

Okay
That is also fairly simple too - with a couple of heads up thrown in.

The plastic dash housing/fascia has about 6 phillips head screws that can be located with a quick look.
The top edge has hidden "metal clips" that snap out - with just a little bit of force applied - pulling it upwards.
You might elect to use a wooden paint paddle as a pry tool to pop them loose if they seem stubborn.

The instrument gauge/cluster also has about 6 phillips screws in plain view (after dash housing is removed)
But FIRST
You have to un-snap the speedo-cable from back of the speedo.

SECOND
You have to unhook the thin cable that makes the gear selector indicator move when you move the shifter. (PRNDSL)
It connects on top of the steering column - just below the sight line of the dash.
If you aren't familiar with these gizmos - look from underneath the dash up to the top of the steering column - move the shifter a bit back and forth and you will see the stob that moves along with it on top of the column.
The cable (actually more like fishing string) has a metal clasp at the end that hooks over that stob.
Unhook the clasp from the stob.
The cable is spring loaded - but only retracts a small amount. Nothing will go funky with it.
Just have the the Van in Park when you go to unhook it / re-hook it

If you forget to unhook it - you will likely ruin the PRNDSL indicator .

2 main wiring connectors can be removed from the backside of cluster once you have it pulled out a bit.
There is a 3rd small connector that goes to the oil pressure Warning Light - i left it alone.
It seemed squirelly so i just left it alone instead of breaking it.
You can still get the cluster completely out of the way even with that oil warning light left plugged in.

Check all the dash lights and indicator lights the night before and see if you need any new bulbs.
Bulb #194 or similar

Good Luck on your Witch Hunt