Question about something in the Coach Battery Box

It could be a battery disconnect. One large terminal adapted to the battery terminal two large wires leaving, two wires to energize.
Is there any markings on the item in question?
What is make and model of the rig?

Does not look like a shunt to me

enblethen wrote:
It could be an amp meter shunt. Is there an amp gauge inside the rig for the house batteries?

That would be my guess as well, Not big enough for a disconnect relay and that is typical of a shunt install.

Often you have

Battery negative---big wire--shunt--chassis. or optionally

Battery negative--Big wire---Shunt--Another big wire---Chassis.

Shunt may also be in the positive side, and will have 2 SMALL wires hooked to it.

I think some spring cleaning is in order

Where do the cables come from or go to?

I assume it would be the aux start relay to connect the house and chassis batteries together to boost start the main engine. Have someone push the switch while you listen for a click.

It could be an amp meter shunt. Is there an amp gauge inside the rig for the house batteries?

well if those big battery cables are connected to it
I would say that is a battery disconnect switch/relay