[Richard]

Thanks for the follow up. Those are indeed six packs. Someone has retrofitted the six packs to the coach. It came with a different style manifold originally. I can see the old screw holes where the original was mounted.

I notice that one of your brake tank gauges is also dropping. That could be because of the leak at the relay valve.

I am sort of guessing this is a new to you coach, and you are on the journey to making it roadworthy. So I am going to give you a few links providing the fundamentals of how the system works. With your background you will be able translate the fundamentals into how the switches should be wired.

https://www.hwhcorp.com/ml20635.pdf

http://www.newellowner.com/newell-air-system/

Your situation is actually easier to troubleshoot because you have toggle switches instead of the HWH control panels.

Here are some key takeaways;
The Height Control Valve is BEFORE the six pack. The travel solenoids must be open for the HCV to automatically control the height.
When the key is OFF, the air bags should be isolated from the rest of the system. Translation, a leaking supply gauge and a dropping corner are NOT the same leak(s).
When checking the actuation of a solenoid, a steel washer should stick when actuated.
You are going to need to fabricate an air system isolator to temporarily install between the six pack and an air bag to understand what is leaking. https://newellgurus.com/showthread.php?t...D+isolator

Don’t hestitate to ask specific questions. We are here to help. The above reading should get you started.