The Dash lites and Radio/A/C cluster lights stay On, though I can dim them with the Dimmer on the Headlight switch. I unplug the headlight switch and everything works normally, Until I press on the brake pedal. Then the dash lights are back on ?

Possible Headlight switch ? All fuses are ok.

 

i had a crazy similar situation, mice made a nest in fuse box under hood and pissed on everything shorting stuff out

 

Been there seen that as Mice or ? chewed on the Cruise enable wire... ]

In disconnecting the Headlight switch again, I can get the dash lights to reset sometimes, not all the time. I seen that with the headlight switch Disconnected, the Dash/Radio lights are always ON. Also when turning off Key, Radio is still on no matter if dimmer has Dash lights dimmed or not ?

 

It was a 2003 2500 I had the problem on, it always drained battery over a couple hrs, then a no start happened, realized dash was staying on along with a lot of other components- when finally finding the issue the headlights would stay on also when connecting the battery. Basically everything came on without the key in the ignition

fuse box was $5xx from dealer

on the underside of it, was corrosion on all the terminals (sorry nest was under the box, not just under the cover, sorry for confusion)

 

Finally fixed the problem. Ordered a Headlight switch to try and sure enuff, fixed the problem !