Dean, you are correct that the lower manifold with the adjustable pressure is the tag axle. My '92 drive axle solenoids look like your tag axle solenoids and I know that Newell still had solenoids that were virtually identical as of a couple of years ago (the new ones did not have the brass cover on them) so it may be that someone replaced the solenoids on your drive axle.
On the front manifold, the black tube is the air release. If a down solenoid is activated, it will, by design, vent air. If it is leaking air all the time, you have a down solenoid that is not seating properly. It could have some 'junk' in it but it is likely a defective solenoid, especially since the two outboard solenoids are getting warm. They should not be getting any current UNLESS the system is telling them to open and even then they shouldn't be open long enough to get very warm. I don't know if Newell used the HWH standard wiring colors or if someone else has modified them since, but the standard HWH wiring is yellow-RF raise, blue-RF lower, gray-travel, white-LF raise, red-LF lower.
In the rear the HWH standard wiring is gray-travel, brown-lower, orange-raise, purple-lower, green-raise. If you think it will help, I can sketch out which wire colors go to which solenoid on my coach, just let me know.
Can you manually raise or lower either the front, rear, right or left from the control panel? If so, you can tell which solenoids are likely defective. If not, there may be a problem with the HWH control circuit board. If you disconnect the positive lead to each solenoid and apply 12 volts, you should be able to get some raising or lowering from each solenoid.
Do you have air leveling and hydraulic jacks or air leveling only. I have air leveling only but I have driven a '92 that had both.
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