Disconnected all batteries (chassis and house) and turned off all disconnect switches yesterday to weld on the broken tag shock upper mount (good thing to check, found this by accident).

On reconnection and switching everything back on, an alarm sounded under the driver's left switch panel, found the source of it in the 24V panel uppermost row of relays, small round. Stopped when key turned to the on position and then started up again. Stopped after about 2 minutes. Just a system reset or?